"Certainly we are aware that he has expressed a desire and an intent in the past to depart Syria".
He is expected to tout USA successes in Syria when he appears before a joint session of Congress to deliver a State of the Union speech at 9 p.m. on Tuesday (0200 GMT on Wednesday).
"Absent sustained (counterterrorism) pressure, ISIS could likely resurge in Syria within six to 12 months and regain limited territory", the report from the Pentagon's inspector general said.
The U.S. Senate passed a Mideast policy bill on Tuesday including a measure that would allow states to penalise businesses that take part in boycotts of Israel and an amendment that breaks with President Donald Trump by opposing any plans for an abrupt withdrawal of troops from Syria.
A top U.S. general warned on Tuesday that Islamic State would pose an enduring threat following a planned USA withdrawal from Syria, saying the militant group retained leaders, fighters, facilitators and resources that will fuel a menacing insurgency.
"It is important to understand that even though this territory has been reclaimed the fight against ISIS and violent extremists is not over and our mission has not changed", the general said, using another name for Daesh. In Baghdad, the once heavily fortified Green Zone enclave for government bodies, worldwide organisations and embassies has been opened up for the first time in years.
It called on the Trump administration to certify conditions had been met for the groups' "enduring defeat" before any significant withdrawal from Syria or Afghanistan.More news: Trump to Call on Democrats to ‘Heal,’ and Bashes Pelosi Over Wall
Trump's decision to leave Syria, which he initially said would be rapid but later slowed down, shocked us allies led to the resignations of Defence Secretary Jim Mattis and the top envoy to the anti-ISIS coalition, Brett McGurk. The withdrawal was later delayed but as Monday's report pointed out, it is now an ongoing process.
Fears that Islamic State fighters are making strategic manoeuvres ahead of a U.S. pullout could also fuel criticism that Trump is telegraphing his military plans - the same thing he accused President Barack Obama of doing in Afghanistan.
Four US troops were killed in an ISIS claimed suicide attack in northern Syria in mid-January. Remember the USA had acted in a similar manner in the nineties as well.
Votel was asked at Tuesday's hearing whether he was asked for his advice about a Syria withdrawal before Trump announced his decision.
Senators voted 70-26 for the amendment sponsored by Senate Majority Leader Mitch McConnell. The text warns that "a precipitous withdrawal" of soldiers could "allow terrorists to regroup, destabilize critical regions and create vacuums that could be filled by Iran or Russian Federation".
The bill and its easy passage show the deep discontent caused by the policies within the president's own Republican ranks.
The bill also includes provisions supported by both Republicans and Democrats to impose new sanctions on Syria and guarantee security assistance to Israel and Jordan.