Sen. Angus King, I-Maine, asked: "So you weren't consulted before that decision was announced?". But he added that he and others in the high command knew in general terms of Trump's "desire and intent in the past to depart Iraq, depart Syria".
Votel warned that ISIS could regroup with the removal of USA troops, meaning the military will have to "keep pressure on this network" even after withdrawal.
Votel noted the fight against Daesh is not over, despite the withdrawal of troops.
He added that territory under Islamic State's control had been reduced to less than 20 square miles (52 square kilometers) and would be recaptured by US-backed forces prior to the American withdrawal, which he said would be carried out in a "deliberate and coordinated manner".
U.S. President Donald Trump is expected to declare near-total triumph over ISIS in Syria in his State of the Union address Tuesday, but American defence officials are increasingly fearful that the militants are simply biding their time until the Americans leave the battlefield as planned.
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.
That pronouncement, however, seems to be opposed by many analysts, intelligence officials and politicians, including close allies of the ruler, who expressed concern about the impact the withdrawal may have on the US role in the Middle East.
In December, Trump tweeted, "We have defeated ISIS in Syria, my only reason for being there during the Trump presidency".
On Monday, the Pentagon published a report which said Daesh could make a resurgence in the region without counterterrorism pressure.
A decision on troop pullout, especially in case of Afghanistan, needs to be taken now so that its implementation could coincide with the time when the election activity in the United States is in full swing, and President Trump could tell the American voters that he did what he pledged, and score political points in his bid to get re-elected as president of the world's sole superpower.
The Defense Department watchdog report warned that even with the Islamic State forces on the run, the group "is still able to coordinate offensives and counter-offensives, as well as operate as a decentralized insurgency".
It said the group was interested in attacking aviation and using chemical, biological, radiological and nuclear materials and that there were up to 18,000 Islamic State militants in Iraq and Syria, including up to 3,000 foreign fighters.
USA officials in recent weeks say Islamic State has lost 99.5 percent of its territory and is holding on to fewer than 10 square kilometres of turf in Syria - an area smaller than New York's Central Park.