WASHINGTON • A task force has been set up to reunite migrant families divided at the Mexican border under US President Donald Trump's "zero tolerance" approach, a report said, as opposition Democrats have kept up the pressure against a "barbaric" policy.

Mr Trump last Wednesday ordered an end to the family separations which have sparked domestic and global outrage, but the fate of the more than 2,300 separated children remains unclear.

United States Secretary of Health and Human Services Alex Azar issued an order last Friday to create the task force, the Politico website reported, citing an internal document it had obtained.

Reflecting the breadth and complexity of the challenge, the document orders the department's preparedness and response office - which deals with emergencies and public health disasters - to assist its refugee resettlement office with the effort.

Politico quoted department spokesman Evelyn Stauffer as saying that Mr Azar was "bringing to bear all the relevant resources of the department in order to assist in the reunification or placement of unaccompanied alien children and teenagers with a parent or appropriate sponsor".

The department did not immediately respond to an Agence France-Presse request for confirmation.

In an effort to staunch the flow of tens of thousands of migrants from Central America and Mexico arriving at the southern boundary every month, Mr Trump had last month ordered that all those crossing the border illegally would be arrested, and their children held separately.

In an about-face, he then ordered an end to the splitting up of parents and children, saying that it was administration policy to "maintain family unity... where appropriate and consistent with law and available resources".

About 500 children have already been reunited with family members, CNN reported, quoting border officials.

Democratic lawmakers kept up the pressure last Saturday, with roughly two dozen of them again visiting a detention facility where children are being held.

Ms Jackie Speier, a California congresswoman, toured the facility in McAllen, Texas, with the group. In a televised news conference, she said she saw children "under the age of five who were segregated from their parents and were crying... They're in cells and in cages".

Another California congresswoman Barbara Lee called the Trump administration's immigration policy "barbaric", adding that the children were traumatised.

Protest marches were scheduled over the weekend in several cities, and advocacy groups including the Human Rights Campaign and the American Civil Liberties Union are calling for a nationwide "Families Belong Together" protest on Saturday this week.

The biggest demonstration was planned for Lafayette Square, across the street from the White House.

It remains unclear how quickly reunions can be carried out. Lawyers working to bring families back together said they were struggling through a labyrinthine process - while more migrants continue to arrive.

Nearly all of the arriving families have officially requested asylum, citing the high levels of violence in their home countries.

The Pentagon is making contingency plans to house thousands of arrivals on US military bases. Defence Department officials said as many as 20,000 could be sheltered on bases in Texas, Arkansas and New Mexico if need be.

The separations have reportedly sparked intense debate even within the White House, leaving widespread confusion about the road forward.

AGENCE FRANCE-PRESSE