Trump keeps Obama's envoy for countering Islamic State

US president Donald Trump will retain his predecessor's special envoy to the coalition fighting the Islamic State group, Brett McGurk, his spokesman said on Thursday.

As "Special Presidential Envoy", McGurk coordinates with around 70 allied states and with regional militia on the ground in the battle to destroy the extremist group in Iraq, Syria and beyond.

A veteran diplomat, he was appointed in November 2015, working out of an office in the State Department and making regular trips to the region.

Trump's administration made it clear that it expected former president Barack Obama's political appointees across the US government to clear their desks on Friday after Trump was sworn in.

But on Thursday, Trump press secretary Sean Spicer said that around 50 high-level names would stay on, including McGurk and some others in vital national security roles.

McGurk was appointed to his current coalition role by Obama, but had previously served former Republican president George W. Bush as his special assistant and senior director on Iraq and Afghanistan.

The other officials staying on include the highest-ranking career officials at key national security agencies like the Pentagon and State Department.

Deputy Defense Secretary Robert Work and America's third-ranking diplomat, Under Secretary of State for Political Affairs Thomas Shannon, will serve as acting chiefs of their agencies until successors for the top jobs are confirmed by the Senate.