Roberta Jacobson, special assistant to the President and coordinator for the southwest border, will "engage with Mexican government officials to develop an effective and humane plan of action to manage migration", Xinhua news agency quoted National Security Council (NSC) spokesperson Emily Horne as saying in a statement on Monday.

Jacobson will be joined by Juan Gonzalez, the NSC's senior director for the Western Hemisphere; and Ricardo Zuniga, the State Department's special envoy for Northern Triangle, which comprises the three Central American countries of Guatemala, Honduras and El Salvador, according to the statement.

From Mexico, Gonzalez, accompanied by Zuniga, will go to Guatemala, where "he will meet with Guatemalan government officials, as well as representatives from civil society and non-government organisations to address root causes of migration in the region and build a more hopeful future in the region", Horne said.

The visits came as pressure continued mounting on the Biden administration over its management of the southern border, where the number of unaccompanied migrant children kept rising at a staggering pace, putting extra strain on a government system to accommodate them.

According to a report by CBS News on March 20, the number of unaccompanied migrant children currently detained in Customs and Border Protection (CBP) facilities has topped 5,000, in addition to another 10,500 or so being placed in emergency housing facilities or state-licensed temporary shelters by the Department of Health and Human Services.

US law dictates that the detention period for such migrant minors in CBP facilities should not last beyond 72 hours, but the CBS News report, citing government records, said that the children currently are spending an average of 136 hours in those facilities.

Biden, whose administration has most recently been criticized for blocking press access to the CBP facilities, told reporters on Sunday that he would travel to the border himself "at some point", adding that he was aware of "what's going on in those facilities".

The President said his administration is in the process of urging the immigrants to "stay in place and make their case from their home country".