WASHINGTON — As President Donald Trump prepares to reaffirm in Tuesday night's State of the Union address both victory over Islamic State and a call for withdrawing American troops from foreign battlefields, a new Pentagon report says the terrorist group is still strong and would get stronger once U.S. troops leave Syria.

A U.S.-led coalition has eliminated some 99 percent of the territory in Syria and Iraq that the Islamic State, or ISIS, once claimed as its so-called caliphate.

But the group remains active and still numbers in the thousands in Syria and Iraq, and it is probably adding about 50 new members a month, the Defense Department inspector general report says. The group's command organization is intact. Its fighters are “battle-hardened.”

Significantly, the Kurdish-led Syrian resistance forces who are fighting Islamic State are essentially unable to conduct offensive operations without U.S. military air support, the report says. Islamic State would depict a U.S. pullout from Syria as a win in its global propaganda outlets. And within a year, U.S. military commanders told the IG, Islamic State would be resurgent in Syria.

NBC News first disclosed the IG's fundamental finding. But key unreported details from the report paint a fuller picture of Islamic State as a scourge that is latent in both Syria and Iraq and ready to metastasize anew.

The report comes as Trump is expected to call in Tuesday's speech for conclusions to what he will describe as endless wars, not just in Syria, where about 3,000 U.S. troops are said to be stationed, but also in Afghanistan, where some 14,000 U.S. military personnel are still deployed.

Trump announced in December that “all” U.S. forces would be leaving Syria “now.” But the troops have yet to start leaving Syria, and officials subsequently have said the military exodus would unfold over several months.

Trump also tasked the Pentagon late last year to start making plans for cutting the U.S. force in Afghanistan in half.

In an interview with CBS News broadcast on Sunday, Trump said the U.S. troops in Syria would be departing soon. He allowed, though, that America would still retain forces in Iraq who would be ready to strike a resurgent Islamic State in Syria or Iraq — something that military commanders have reportedly been pressing for as a hedge against Islamic State's resurgence. Trump also said U.S. forces in Iraq could form a check on neighboring Iran.

There are about 5,000 U.S. troops still in Iraq.

“When I took over Syria it was infested with ISIS — it was all over the place — and now you have very little ISIS and you have the caliphate almost knocked out,” Trump said in the interview. “At the same time, at a certain point, we want to bring our people back home.”

Starting this week, the new Congress is stepping up its oversight of U.S. military operations in Syria, Iraq, Afghanistan and Africa, and the planned drawdowns of troops from several of those places.

Army Gen. Joseph Votel, the chief of U.S. Central Command, who oversees U.S. military operations in the Middle East and Southwest Asia, will be asked direct questions about the planned withdrawals from Syria and Afghanistan — including the risks involved — in testimony scheduled for Tuesday before the Senate Armed Services Committee.

Meanwhile, the House Armed Services Committee, now under Democratic control, plans a Feb. 6 hearing to examine U.S. counterterrorism operations more broadly, with testimony expected from Owen West, the Pentagon's assistant secretary for special operations and low-intensity conflict, and Air Force Maj. Gen. David Allvin, the Joint Staff's vice director of strategy, plans and policy.

The Islamic State issue will also come up at a Feb. 6 Senate Armed Services hearing on global threats. Director of National Intelligence Dan Coats and Defense Intelligence Agency Director Lt. Gen. Robert Ashley are scheduled to testify.

The inspector general's assessment is a quarterly report on the fight against Islamic State. It was updated last month after the president's announcement about a Syria withdrawal.

According to the IG report, most of the military commanders' replies to the IG's January questions were classified, but Votel's command provided one overarching conclusion that was not classified.

“ISIS remains an active insurgent group in both Iraq and Syria,” the command wrote. “If Sunni socio-economic, political, and sectarian grievances are not adequately addressed by the national and local governments of Iraq and Syria it is very likely that ISIS will have the opportunity to set conditions for future resurgence and territorial control. Currently, ISIS is regenerating key functions and capabilities more quickly in Iraq than in Syria, but absent sustained (counterterrorism) pressure, ISIS could likely resurge in Syria within six to twelve months and regain limited territory in the” Middle Euphrates River Valley.

The command added that Islamic State “may conduct opportunistic attacks on U.S. personnel as they withdraw” and posited that the group's leaders “will leverage the event as a 'victory' in its media.”

According to the joint military task force that has been fighting Islamic State for more than four years, the group remains “a battle-hardened and well-disciplined force” that is “able to coordinate offensives and counter-offensives,” the inspector general reported.

Islamic State's leadership, meanwhile, retains “excellent command and control capability” in Syria, the task force reported, according to the IG. Islamic State “remained able to plant bombs and carry out assassinations throughout Syria.”

The task force also told the IG that, “in preparation for the complete loss of territory, Islamic State increasingly functions as a decentralized insurgency as its 'way ahead plan.'”

As for the number of remaining Islamic State fighters in the region, the military's answers to the IG are classified. But figures from the U.S. military and a United Nations agency have ranged between 20,000 and 32,000 — though officials have acknowledged lacking confidence in their estimates.

Islamic State “continues to attract foreign fighters” at a rate of “most likely 50 per month,” the task force said. The report does not address any attrition in Islamic State's ranks.

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