President Biden's pressure on Israel after last week's deadly attack on aid workers did not go far enough and will fail to stem the humanitarian crisis in Gaza, according to current and former US officials who have spoken to the BBC.

They said internal dissent in government was growing and called for tougher action on arms transfers.

Israel said it would open new aid routes after President Biden threatened to reassess policy following Israeli strikes that killed seven workers from food charity World Central Kitchen (WCK), including a US citizen.

But the tougher line was "too little, too late", said Annelle Sheline, an official working in human rights who quit the state department in protest a fortnight ago.

She said the White House "could have done this months ago and prevented famine in northern Gaza".

The US-Israel relationship is currently experiencing its most serious strain in decades, after President Biden's phone call with Israeli Prime Minister Benjamin Netanyahu last week that amounted to a defining moment in the six-month conflict.

Within hours of Mr Biden's call, Israel said it would open the Erez crossing in northern Gaza and the port of Ashdod in southern Israel to aid, and pledged to drastically improve security co-ordination with groups delivering assistance to Palestinians.

Watch: US says Israel must make changes in the coming "hours and days"

In a newly-aired interview, Mr Biden said he believed the Israeli prime minister was making "a mistake" in his handling of Gaza.

The US president spoke to Univision two days after the Israeli strike on WCK workers - and before Israel announced the opening of the Erez crossing - though the footage was only aired on Tuesday,

In the interview, Mr Biden said he said his ally should "just call for a ceasefire" with Hamas, and allow "total access to all food and medicine" for Gaza.

Despite the steps taken by Mr Netanyahu last week, the views of seven current and former US government officials reflect the way internal objections to policy continue to mount. They said many government workers were voicing their frustrations in unofficial forums that include at least a dozen groups on messaging apps, which the officials said counted hundreds of administration staff as members.

A spokesperson for the US state department said it encouraged different views on policy and staff could make them known through "appropriate channels". The US had "been clear at the highest levels publicly and privately with Israel that it must abide by international humanitarian law", the spokesperson said.

Israel doing the bare minimum, official says

Four current officials at varying levels of seniority in different government departments spoke to the BBC on condition of anonymity. Two have roles in areas with direct links to foreign policy, including on Israel and Gaza.

One who has 25 years of national security experience said internal opposition had become "deeper, wider and more despairing" than at any previous point in the war. While the increase in pressure from President Biden last week was welcome, it did not go far enough to reflect the "moral urgency" to act, they said.

"I read it as Israel doing the bare minimum to get through the day and avoid arms transfers being halted," the official added.

Secretary of State Antony Blinken has made five trips to Israel since the 7 October attack

US Secretary of State Antony Blinken said on Tuesday more than 400 trucks had been cleared to go into Gaza the previous day, describing "important commitments" made by Israel. However, UN officials told the BBC the figure was in fact 223, less than half the daily number it says is required as a minimum to stem the crisis.

Some of the officials who spoke to the BBC said they wanted the Biden administration to explicitly condition arms supplies to Israel in order to avoid a full-scale humanitarian collapse.

The administration has been under increasing pressure to say whether it is conducting a full review by the state department's Office of the Legal Advisor into whether Israeli actions in Gaza have breached international law, which could lead to a bar on US weapons shipments.

Josh Paul, a former senior official who resigned last year in protest, said the state department had not asked the office to make an assessment because "it does not want the answer it will get". The state department declined to confirm whether it had referred any cases to the office.

Jose Andres says Monday's strike which killed seven members of his staff was not a mistake.

The officials' concerns echoed those of dozens of Democrats in Congress, including Biden ally and former House Speaker Nancy Pelosi - who signed a letter on Friday urging the US to pause weapons' transfers to Israel in the wake of the 1 April strikes on the WCK aid convoy, which sparked international outrage. The Israeli military called the attack a "grave accident".

Israel has consistently denied violating international law in Gaza, blaming thousands of civilian deaths from its offensive on Hamas for operating from civilian areas. It says it has fought a threat to Israel's existence after the attacks by Hamas on 7 October, in which some 1,200 people were killed and more than 240 were taken hostage back to Gaza.

The three former officials the BBC spoke to include Ms Sheline and Mr Paul, who both quit in protest, and Brian Finucane, a lawyer who spent a decade at the state department advising on laws of war and arms transfers.

Civil servants find avenues for dissent

There has been ongoing dissent within the US government about Gaza policy since the first months of the war. And in February, hundreds of civil servants in the US and European countries warned that their governments risked being complicit in "grave violations of international law" in a letter initially obtained by the BBC.

At the time, Robert Ford, a former US ambassador, said that unlike during the lead-up to the 2003 US invasion of Iraq, when many officials had reservations but did not speak up, the seriousness of Gaza war had pushed career civil servants to publicly air their concerns.

A second serving US official who spoke to the BBC anonymously described ongoing exchanges in at least a dozen chat groups on messaging apps Signal and WhatsApp. In these, staff vented exasperation and incredulity at the way they perceived the Biden administration too easily accepted Israeli versions of events.

"There's a lot of eye rolling... People can point out the inconsistencies and the fallacies pretty quickly," said the official.

The World Central Kitchen aid workers killed on 1 April had been transporting food aid delivered by sea into Gaza while Israeli-controlled land routes remained tightly restricted.

A "foolish" system of deliveries by sea, as well as plans for a US-built floating pier to get aid in Gaza, were both designed "as a workaround for the fact that we [did] not pressure the Israelis to let aid in other ways", said the official who has spent more than two decades working in US national security.

After Israel's announcement on aid routes on Thursday, Mr Blinken said Washington would judge the move by "results" in protecting civilians.

Israel has previously blamed the United Nations for aid delivery failures - a claim categorically rejected by the UN and humanitarian groups - and has said Hamas steals supplies.

A third government official said the fact that much more concerted US pressure was applied only after the deaths of international aid workers sent a message that "Palestinian lives do not matter". Nearly 200 Palestinian aid workers have been killed in Gaza since the start of the war, according to Humanitarian Outcomes, a group that monitors aid-worker deaths.

Concern over US weapon transfers

The officials' accounts are the latest sign of deepening disquiet and a growing readiness within the ranks of the Biden administration to question the moral and legal basis of US backing for Israel, a bedrock of Washington policy going back decades across administrations. Some criticised the support as apparently unconditional, citing Washington's $3.8bn (£3bn) a year package of military assistance to Israel and the potential sale of $18bn worth of F-15 fighter jets.

The supply of arms has continued uninterrupted despite the number of people killed in Gaza now standing at more than 33,000, according to figures from the Hamas-run health ministry, which are accepted by the US government.

In a recent statement, the Israeli military said it had killed about 13,000 Hamas fighters since the start of the war, although it did not say how it calculated that figure.

It has consistently denied killing large numbers of civilians, either deliberately or through negligence. But accusations of reckless targeting have continued to grow, leading to calls in the US for an assessment over whether Israel's military campaign was in breach of international humanitarian law, which prohibits the targeting of non-combatants.

State department spokesman Matthew Miller said last week that the US had "not at this time concluded that Israel has violated international humanitarian law" but said its assessments were "very much ongoing".

But referring to the assessments, Mr Finucane, the former state department lawyer, told the BBC: "I think they're likely dramatically overstating the reality."

He described a new process the department launched in September to monitor any civilian harm by partner military forces as essentially "guidance" with "no structure behind it".

Since the dissent letter by officials in February, US policy has still lacked "course correction despite its manifest failures", according to Mr Finucane, who is now a senior advisor at the International Crisis Group.

Responding to the criticism, the state department spokesman said that Mr Blinken "takes all feedback and opinion seriously, and it causes him to reflect on his own thinking in terms of policymaking".