President Donald Trump signed an executive order Wednesday that he says will keep migrant families together during detention on the U.S.-Mexico border.

The president backed down from his administration's policy of splitting migrant families, which for days the White House insisted could only end through congressional action. Facing a nationwide uproar and bipartisan calls to at least temporarily end the practice, the president said he "didn't like the sight or feeling of families being separated."

Trump said he will not end the administration's "zero tolerance" policy of criminally prosecuting every adult who crosses U.S. borders illegally, including those seeking asylum. The White House also will keep pressure on Congress to pass legislation that meets Trump's goals of halting the separation practice, funding his proposed border wall and limiting legal immigration.

"We're keeping families together and this will solve that problem. At the same time we are keeping a very powerful border and there continues to be a zero tolerance," Trump told reporters before he signed the order.

It was not immediately clear Wednesday what would happen to the children already separated from their parents. The order did not appear to address how the government would go about reuniting families.

Reuters later reported that House Republicans briefed on the order by Homeland Security Secretary Kirstjen Nielsen worried the measure would not prevent family separations during detentions longer than 20 days.