WASHINGTON (Reuters) - The new chief of the Department of Homeland Security (DHS) named the United States’ top airport-security official, David Pekoske, his acting deputy on Thursday, as President Donald Trump overhauls the leadership of the domestic-security agency.

The move, by Acting DHS Secretary Kevin McAleenan, who took office on Wednesday, temporarily fills a leadership vacuum at the top of DHS, which is responsible for everything from border protection to disaster response.

But it also places further strains on an agency of 240,000 employees, many of whose top leadership posts were unfilled even before Trump’s management shakeup.

McAleenan remains in charge of U.S. Customs and Border Protection even as he assumes responsibility for all of DHS.

Likewise, Pekoske will continue to head the U.S. Transportation Security Administration, which screens airline travelers, while he serves as the No. 2 official at DHS. Both men are serving on a temporary basis.

In recent weeks, Trump has interviewed several candidates for DHS secretary, an appointee who must be confirmed by the Republican-controlled U.S. Senate.

Trump has forced out top DHS officials over the past week as the agency tries to stem rising numbers of immigrants arriving at its southern border, many of them families fleeing violence and poverty in Central America. DHS said it arrested or denied entry to more than 103,000 people along the border last month, more than double the figure for March 2018.

Trump has grown increasingly frustrated as DHS officials have told him that dramatic immigration changes he wants are not possible under current law, several sources say.

DHS Secretary Kirstjen Nielsen announced her departure on Sunday after clashing with Trump over border security. Her deputy, Claire Grady, stepped down on Tuesday.

Trump is trying to force out L. Francis Cissna, who oversees legal immigration programs as director of U.S. Citizenship and Immigration Services, as well as John Mitnick, the top DHS lawyer, according to a source familiar with White House deliberations.

Leadership is also in flux at U.S. Immigration and Customs Enforcement, the U.S. Secret Service and the Federal Emergency Management Agency (FEMA). Ten other top positions are either vacant or filled on a temporary basis.