President Donald Trump says Chad Wolf, a longtime Homeland Security official, will become the new acting head of the department, the fifth person in the job for this administration.

Key points: Current acting head of the department, Kevin McAleenan, was expected to stay in the role

Current acting head of the department, Kevin McAleenan, was expected to stay in the role Chad Wolf has served in both Democrat and Republican administrations and is well respected

Chad Wolf has served in both Democrat and Republican administrations and is well respected He is considered to have a softer approach to immigration

But Mr Trump's casual announcement, made in response to a reporter's question outside the White House, temporarily created more uncertainty about who was in charge of the sprawling agency.

Weeks of speculation focused on who would be named the next leader, and Kevin McAleenan, the current acting secretary, had agreed to stay on temporarily. The department initially would not confirm Mr Wolf was next in line, saying only that Mr McAleenan was acting secretary.

When a reporter asked Mr Trump directly whether Mr Wolf was to be the next DHS secretary, the President responded, "He's acting, and we'll see what happens."

President Donald Trump casually announced Chad Wolf's appointment when he was asked by a reporter about it. ( AP: Evan Vucci )

White House spokesman Hogan Gidley later clarified: "As the President has said, Mr McAleenan has done a tremendous job. He'll be leaving after Veterans' Day and after he departs, Chad Wolf will serve as acting secretary in the interim."

The elevation of Mr Wolf, who has served in Democratic and Republican administrations, is likely to disappoint immigration hardliners and perhaps Mr Trump himself. The White House had been trying to work around rules that prevented Mr Trump from promoting several political allies to at least temporarily run the agency, which carries out US immigration policies.

Mr Wolf was chief of staff to former DHS Secretary Kirstjen Nielsen. He has been involved with the 240,000-person department off and on since its creation following the September 11, 2001, terrorist attacks.

'A proven, thoughtful and principled executive'

Mr Wolf worked with Ms Nielsen through many of the administration's most challenging immigration issues but left as her chief of staff to take on another role within Homeland Security before she resigned in April.

He was nominated earlier this year to a Senate-confirmed position as under secretary of the department's Office of Strategy, Policy and Plans. That nomination has not been yet confirmed.

He is described by some colleagues as a knowledgeable and widely respected member of the department, who can carry on the President's agenda. In a statement issued on Saturday (local time), Mr McAleenan praised Mr Wolf as "a proven, thoughtful and principled executive".

But he was not initially discussed as a successor.

For weeks, various factions have been looking for legal blocks and workarounds as they sparred over who was eligible to succeed Mr McAleenan. Federal vacancy rules that place restrictions on the position had been thought to bar immigration hardliner Ken Cuccinelli, currently the acting head of US Citizenship and Immigration Services, and Mark Morgan, the current acting commissioner of US Customs and Border Protection, from taking the job.

But officials recently identified a "loophole" in which Mr Trump could appoint otherwise ineligible individuals by first tapping them to lead the Countering Weapons of Mass Destruction Office — a post that is vacant.

It is possible Mr Wolf could take over temporarily while the work-around is put into place.

The massive department was initially envisioned as a cohesive counterterrorism operation. It includes the Coast Guard as well as disaster relief and election security. However, Mr Trump has been strongly focused on immigration issues, which were a key theme of his 2016 election campaign.

Reuters