Trump aims for Syria pullout but aides say 'mission isn't over'

US President Donald Trump said on Tuesday he wanted to "get out" of Syria and promised decisions soon, even as his advisers warned of the hard work ahead to defeat the Islamic State (IS) group and stabilise areas recaptured from the militant group.

Trump's remarks suggested he believed that the US military-backed campaign against IS in Syria was close to being complete. The Pentagon and State Department, however, have suggested a much longer-term effort is necessary.

"It's time," Trump told reporters. "We were very successful against (IS). We'll be successful against anybody militarily. But sometimes it's time to come back home, and we're thinking about that very seriously."

The United States has about 2,000 forces in Syria who are battling the group.

US Army General Joseph Votel, who oversees American troops in the Middle East as the head of Central Command, estimated on Tuesday that more than 90 percent of the group's territory in Syria had been taken back from the militants.

Trump estimated that the percentage of territory recaptured in Iraq and Syria at "almost 100 percent," and, in a sign of his complicated views on the campaign, also said: "We will not rest until ISIS is gone."

However, Brett McGurk, the special US envoy for the global coalition against IS, speaking alongside Votel on Tuesday, said the fight against the militants was not over.

"We are in Syria to fight ISIS. That is our mission and our mission isn't over and we are going to complete that mission," McGurk said.

McGurk acknowledged a review was underway to ensure US taxpayer dollars were well spent, when asked about media reports that Trump had ordered the State Department to freeze more than $200m in funds for recovery efforts in Syria.

Trump had said he wants "to start rebuilding our nation," in an implied criticism to foreign aid going to Syria.

Votel said he saw a US military role in stabilisation efforts in Syria.

"The hard part, I think, is in front of us, and that is stabilising these areas, consolidating our gains, getting people back into their homes," Votel said.

"There is a military role in this. Certainly in the stabilisation phase."

In December 2017, the Pentagon signalled an open-ended troop commitment in Syria.

"We are going to maintain our commitment on the ground as long as we need to - to support our partners and prevent the return of terrorist groups," Pentagon spokesman Eric Pahon told AFP news agency then.