A Pakistani army soldier looks at a classroom at the Army Public School and Degree College in Peshawar, Pakistan, on Dec. 17, 2014. Taliban gunmen killed 145 people at the school, many of them children, the day before. (Max Becherer/Polaris for The Washington Post )

Less than two months ago, U.S. troops ended their combat mission in Afghanistan with great fanfare. On Thursday came fresh signs that at least some of the 12,500 coalition troops remaining in Afghanistan remain very much part of the fight.

At a news conference on the outskirts of the Pakistani capital, Islamabad, the chief spokesman for the Pakistani military announced that six Taliban militants were arrested recently during a joint mission by NATO and Afghan troops in eastern Afghanistan. The militants were wanted for organizing the December massacre at a school in Peshawar in northwestern Pakistan.

The news of the arrests is the latest sign of the growing cooperation between Pakistan and Afghanistan in working to combat the threat posed by Islamist militants on both sides of the border. It also demonstrates that U.S. forces remain directly involved in risky missions in Afghanistan.

A coalition spokesman in Kabul confirmed that some foreign troops accompanied the Afghan army on a mission in Nangahar province in eastern Afghanistan on Feb. 3-4. The spokesman said the operation was part of the coalition’s continued “advise and assist role” in supporting the Afghan army.

“All coalition military operations are conducted in accordance with the law of war, rules of engagement and pertinent international agreements,” said the spokesman, referring all additional questions to the Afghan army.

It was not immediately clear whether Pakistani Taliban militants were killed or wounded during the raid. But the United States also considers the Pakistani Taliban to be a threat, one reason that the tempo of drone strikes in Pakistan increased in the weeks after the school massacre.

A security agreement between the United States and Afghanistan authorizes “U.S. military operations to defeat al-Qaeda and its affiliates,” as well as “combined military exercises” between coalition and Afghan troops. Whenever possible, however, Afghan troops are expected to lead those operations, the agreement states.

Such involvement may serve as a blueprint for future American military operations in Iraq.

On Wednesday, The Washington Post reported that President Obama will ask Congress for authorization for the use of military force to help Iraqi forces battle Islamic State militants. The authorization would prohibit offensive ground combat operations but allow ground deployments for rescue missions and assistance to local forces, The Post’s Karen DeYoung reported.

Generally, U.S. forces on bases in both Afghanistan and Iraq are allowed to take defensive action to neutralize possible threats. At times, such threats could involve troops leaving their bases for what amounts to offensive-defensive action.

But while the true extent of American involvement in Iraq remains to be seen, it appears likely that U.S. troops in Afghanistan will continue to help hunt for Pakistani Taliban leaders. Many of them, including top commander Maulana Fazlullah, are believed to reside in eastern Afghanistan.

Since the school massacre, there have been several meetings between Raheel Sharif, Pakistan’s military chief, and Gen. John. F. Campbell, commander of coalition forces. At least for now, Pakistan’s military is ruling out crossing the border into Afghanistan to try to capture or kill the remaining suspects in the Peshawar attack.

But Maj. Gen. Asim Bajwa, chief spokesman for the Pakistani military, said Thursday he fully expects that Fazlullah’s days of freedom are numbered.

“The handing over of Fazlullah is the number one demand of Pakistan from Afghanistan,” Bajwa said. “We hope to have a quick response from them soon."