US President Joe Biden has defended his policy of providing shelter to unaccompanied children crossing the US border from Mexico at a news conference where he was repeatedly pressed on his handling of immigration issues.

Mr Biden also set a new goal of administering 200 million vaccination shots against COVID-19 in the United States in his first 100 days in office and claimed economic progress as he held his first solo news conference since taking office.

Struggling to contain a surge in border crossings, Mr Biden told reporters that no previous administration had refused care and shelter to children coming over from Mexico except that of his predecessor, Donald Trump.

“I’m not going to do it,” Mr Biden said, noting he had selected Vice President Kamala Harris to lead diplomatic efforts with Mexico, Honduras, Guatemala and El Salvador aimed at stemming the migration flow.

Appearing in the White House East Room, Mr Biden said his initial goal of administering 100 million vaccination shots in his first 100 days in office was reached last week, 42 days ahead of schedule.

“I know it’s ambitious, twice our original goal, but no other country in the world has even come close,” said Mr Biden.

Mr Biden said a May 1 deadline to withdraw US troops in Afghanistan will be difficult to meet.

“It’s going to be hard to meet the May 1 deadline,” he said.

But he added, “We are not staying a long time” in Afghanistan, site of the longest war involving the US.