US President Joe Biden has signed three executive actions seeking to reunite migrant families split up by a Trump-era policy and ordering a review of his predecessor's wider immigration agenda.

In an attempt to deter illegal immigration, President Donald Trump's administration separated undocumented adults from children as they crossed the US-Mexico border.

Mr Biden's orders will set up a task force to try to reunite the estimated 600-700 children who are still apart from their families.

The Trump administration split up at least 5,500 children from adults along the border between 2017-18.

The administration of US President Barack Obama - whom Mr Biden served as vice-president - also separated undocumented children from adults at the border, though much more rarely, say activists.

One of Mr Biden's orders will set up an inter-agency task force - led by the newly confirmed Secretary of Homeland Security Alejandro Mayorkas - to oversee family reunifications

Mr Biden's second and third orders signed on Tuesday order a review of Mr Trump's immigration policies that curtailed asylum, slowed legal immigration into the US, and cancelled funding to foreign countries.

Speaking at the White House, Mr Biden said: "We're going to work to undo the moral and national shame of the previous administration that literally not figuratively ripped children from the arms of their families, their mothers and fathers, at the border and with no plan, none whatsoever, to reunify the children who are still in custody and their parents."

Mr Biden has also proposed legislation to grant legal status and a path to citizenship to all of the estimated 11 million undocumented people in the US.

But analysts say the new president has so far avoided reversing Mr Trump's hardline policies in order to avoid a surge in illegal immigration at the southern border.

At Tuesday's White House briefing, press secretary Jen Psaki said the administration was committed to building a "moral" and "humane" immigration system. But until that happened, she added, now was "not the time to come to the United States".

The migrant girl detained by US for 531 days and counting

By Patricia Sulbarán Lovera, BBC Mundo

Nine-year-old Luisa, from El Salvador, is currently the migrant child who has spent the longest time in the custody of US Immigration and Customs Enforcement, according to legal aid organisations.

Luisa sometimes sounds wise beyond her years. She has had to write letters to legislators, asking authorities to release her and Ariana, her mother, from a US migrant detention centre in Dilley, Texas.

Luisa is tired of her situation. "I have spent two Christmases here," she says. "I miss cooking food. I would like to cook my own food. I have learned a little bit of English. I want to learn more at school, but away from here."

Her mother says the girl does not like the food at the detention centre, and that her behaviour has changed as time goes by. "She only eats fruit, and sometimes not even that," she adds.

Ariana, 31, adds that she herself has fallen ill from anxiety.

"I am taking pills, and some time ago I experienced an attack. I did not know what it was. The paramedics told me it was an anxiety attack.

"I sometimes feel like it is not me who is in there."

Activists want bolder action from Biden

By Angélica M Casas, BBC News

As President Biden starts chipping away at Trump-era immigration policies through a series of executive orders, it's still difficult for some immigration advocates to celebrate.

"The expectation is that this administration take bold, decisive action by swiftly reversing policies," says Alejandra Gomez, the co-executive director of Living United for Change in Arizona, a grassroots organisation.

"It's a good first step. But while review of Trump's immigration policies is important, we need action. That's why those of us who can vote elected him."

So far, none of President Biden's orders have directly reversed any Trump immigration policies.

"Our immigrant community experienced a lot of suffering over the last four years," says Ms Gomez.

She says Mr Biden knows what the immigrant community wants.

"We ultimately are seeking to defund Immigration and Customs Enforcement and we are looking for relief and a path to citizenship for 11 million people."

How did family separations come about?

Under a "zero-tolerance" immigration policy adopted in April 2018, adult undocumented migrants crossing the US-Mexico border were criminally charged and jailed.

These offences had previously been treated as civil violations.

Because the children of prosecuted migrants could not legally be charged with any crime, they were not permitted to be jailed with their parents, which led to the youngsters being placed in shelters or foster care.

Images and videos of children on sleeping mats in crowded detention facilities sparked a nationwide furore, leading Mr Trump to halt the policy that June.

Last week, the Biden justice department formally revoked the dormant policy.

However, the chain-link enclosures where some of the children were detained were built during the Obama presidency. Some 60,000 unaccompanied minors stopped at the southern border were detained in these cells during one summer alone back in 2014.

Obama-era officials have said migrant family separations were unusual during his presidency, for example, in cases where there was reason to suspect trafficking, though the exact numbers are unclear.

Mr Obama's top immigration adviser Cecilia Munoz - who in 2011 defended the migrant family separations as the inevitable result of a "broken system" - served on Mr Biden's presidential transition team.