BAGHDAD — U.S. Defense Secretary Jim Mattis said Tuesday he is confident that U.S.-backed Iraqi forces will finish off the Islamic State militants clinging to strongholds that are shrinking in size and number.

“ISIS is on the run,” Mattis told reporters after meeting with Prime Minister Haider al-Abadi and other Iraqi government leaders. “They have been shown to be unable to stand up to our team in combat.”

Mattis spoke alongside Lt. Gen. Stephen Townsend, the top U.S. commander in Iraq, who is due to finish his tour of duty here in early September.

“The fighting is tough,” Townsend said, “but the momentum is with our partners.”

Earlier, Mattis described the extremists as being trapped in a military vise that will squeeze them on both sides of the Syria-Iraq border.

Mattis had arrived in the Iraqi capital hours after President Donald Trump outlined a fresh approach to the stalemated war in Afghanistan. Trump also has pledged to take a more aggressive, effective approach against IS in Iraq and Syria, but he has yet to announce a strategy for that conflict that differs greatly from his predecessor’s.

The Pentagon chief told reporters before he left neighboring Jordan that the Middle Euphrates River Valley — roughly from the western Iraqi city of al-Qaim to the eastern Syrian city of Der el-Zour — will be liberated in time, as IS takes hit from both ends of the valley that bisects Iraq and Syria.

Having enabled Iraqi government forces to reclaim the Islamic State’s prized possession of Mosul in July, the U.S. military effort is showing tangible progress and the Pentagon can credibly assert that momentum is on Iraq’s side.