Barack Obama has endorsed Vice-President Kamala Harris to be the Democratic presidential nominee, ending days of speculation over whether he would support her.

Former President Obama and ex-First Lady Michelle Obama said in a joint statement that they believe Ms Harris has the "vision, the character, and the strength that this critical moment demands".

Mr Obama was reportedly among more than 100 prominent Democrats Ms Harris spoke to after President Joe Biden announced last Sunday he was dropping out of the race.

In a statement at the time, Mr Obama praised Mr Biden's exit, but stopped short of endorsing Ms Harris.

The US vice-president has already secured the support of a majority of Democratic delegates, setting her on course to become the official nominee at the party convention in August.

The Obamas said in Friday's statement that they could not be "more thrilled to endorse" Ms Harris. They vowed to do "everything we can" to elect her.

"We agree with President Biden," said the couple's statement, "choosing Kamala was one of the best decisions he’s made. She has the resume to prove it."

They cited her record as California’s attorney general, a US senator and then vice-president.

"But Kamala has more than a resume," the statement continued. "She has the vision, the character, and the strength that this critical moment demands.

"There is no doubt in our mind that Kamala Harris has exactly what it takes to win this election and deliver for the American people.

"At a time when the stakes have never been higher, she gives us all reason to hope."

The statement was accompanied by a video of Ms Harris taking a phone call from the Obamas in which they pledge their support.

"Oh my goodness," says the vice-president in the clip. "Michelle, Barack, this means so much to me."

Ms Harris has held a number of campaign events across the US in the days since Mr Biden withdrew from the race.

On Thursday, she addressed the American Federation of Teachers union in Houston.

While the event was billed as part of her vice-presidential duties, it had the air of a campaign rally, with loud applause and cheers from the audience.

Echoing language used in campaign events earlier in the week, Ms Harris took aim at what she termed "extremist" Republicans and "failed" policies.

“We want to ban assault weapons, and they want to ban books,” she said.

Meanwhile, Republican presidential nominee Donald Trump continued to pivot to assail his new rival.

"Lyin' Kamala Harris is a radical left Marxist, and worse!" he said in a partially all-capital-letters post on his social media platform Truth Social.

Trump also refused to commit to a televised debate with Ms Harris until she is officially confirmed as the party's nominee.

He suggested Democrats were "still holding out for someone 'better'".

Ms Harris has also had "frank and constructive" talks with Israeli Prime Minister Benjamin Netanyahu, and told him it was time for the Israel-Gaza war to end.

Israel launched a campaign in Gaza to destroy Hamas in response to the attack on southern Israel last October, during which about 1,200 people were killed and 251 others were taken hostage.

More than 39,000 people have been killed in Gaza since then, according to the territory’s Hamas-run health ministry.

Kamala Harris said she made clear her "serious concerns" about casualties in Gaza, telling Mr Netanyahu how Israel defended itself mattered.

Ms Harris also stressed the need for a path to a two-state solution.

The Israeli prime minister also met President Biden while on a trip to the White House, and will meet Republican presidential nominee Donald Trump on Friday.