(CNN) The Pentagon believes ISIS could re-emerge and take back territory in Syria within months if the US does not maintain military pressure on the terror group, according to an official familiar with the latest assessment.

The warning comes as the Pentagon continues to implement President Donald Trump's December order to withdraw all US troops from the country.

A Pentagon report that is expected to be published next week is expected to state that ISIS could regain territory within six months to a year of a US withdrawal. However, some military and intelligence officials are concerned it could happen even sooner, one US official said.

On Tuesday the Worldwide Threat Assessment , released by Director of National Intelligence Dan Coats, stated that "ISIS will seek to exploit Sunni grievances, societal instability, and stretched security forces to regain territory in Iraq and Syria in the long term."

Coats told the Senate Intelligence Committee that "ISIS is intent on resurging and still commands thousands of fighters in Iraq and Syria."

The Pentagon report and Coats' assessment are at odds with claims made by Trump and other senior members of the administration.

When the President announced that US troops would withdraw from Syria in December he declared in a video released on Twitter that "We have won against ISIS. We've beaten them and we've beaten them badly. We've taken back the land and now it's time for our troops to come back home."

Last week, Secretary of State Mike Pompeo touted the gains the US and its partners have made in the fight against the terrorist organization.

"It should not go unnoticed that we've also defeated the ISIS caliphate in Syria and Iraq alongside more than six dozen nations in the Global Coalition to Defeat ISIS," Pompeo said in remarks to the World Economic Forum delivered via satellite.

Trump's withdrawal plans have come under sustained bipartisan criticism. The Senate voted Thursday to advance an amendment highly critical of the President's push to remove troops from Syria and Afghanistan, a rare public admonishment by the Republican-led chamber and Majority Leader Mitch McConnell, who authored the amendment and forced a vote on it.

At this point the US troop withdrawal is expected to be completed within three to four months unless plans change.

A US presence along the northern border with Syria and at the At Tanf enclave in southern Syria near the border with Jordan and Iraq remains under discussion.

There are now more than 3,000 US troops in Syria; around 1,000 extra troops have been sent to help provide security and transportation for the US withdrawal.

Military and intelligence officials have been intent on warning that ISIS's strength does not depend on the amount of territory it holds, but the administration is very focused on what it refers to as the physical caliphate.

"If we wind the clock back two years, I'd say 99.5%-plus of the ISIS-controlled territory has been returned to the Syrians. Within a couple weeks, it'll be 100%," acting Defense Secretary Patrick Shanahan told reporters this week. But he also noted, "ISIS is no longer able to govern in Syria. ISIS no longer has freedom to mass forces. Syria is no longer a safe haven. We've eliminated the majority of their leadership. We've significantly diminished their financial capabilities."