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U.S. troops in Afghanistan lowered the flag and boxed up their gear at the end of last year as President Obama declared the formal end to 13 years of U.S. combat operations.

As far as most Americans were concerned, that brought down the curtain on the longest war in U.S. history, even if the Afghan military and the Taliban were still slugging it out.

But the U.S. airstrike that hit a hospital Saturday and killed 22 civilians in the northern city of Kunduz has returned the spotlight to Afghanistan and the overlooked fact that U.S. forces are still deeply involved in the fighting.

The U.S. military says it has flown more than 3,300 sorties and fired on enemy forces 629 times this year through the end of September.

While U.S. casualties are much lower than in previous years, 14 American military personnel have been killed in 2015. Five deaths were classified as hostile and nine were nonhostile, including six who died when a transport plane crashed last Thursday shortly after takeoff from the eastern city of Jalalabad.

The Taliban takeover of Kunduz, if only for a few days, also raised the specter of Iraq, where U.S. combat troops withdrew completely at the end of the 2011 amid relative calm.

However, the ineptitude of the Iraqi military and the rise of the Islamic State prompted a reluctant Obama to launch a new campaign in Iraq in last year. Airstrikes have achieved limited progress so far and more than 3,000 U.S. forces are now in Iraq, though they are not participating in ground combat.

Obama, who frequently emphasized his decision to end American combat in Iraq, badly wants to avoid having to backtrack in Afghanistan as well.

A Withdrawal, With Caveats

With the Iraqi setback fresh on his mind, Obama inserted a couple of large caveats in announcing the end of U.S. combat in Afghanistan late last year.

First, nearly U.S. 10,000 troops would remain in the country temporarily, and second, they would be permitted to shoot under certain circumstances, including counterterrorism operations and to protect American and Afghan forces.

"The United States — along with our allies and partners — will maintain a limited military presence in Afghanistan to train, advise and assist Afghan forces and to conduct counterterrorism operations against the remnants of al-Qaida," the president said.

However, the line between counterterrorism and ordinary combat is fuzzy, particularly when it involves fighting small, secretive groups like al-Qaida and the Taliban.

In addition to the frequent American air sorties, U.S. Special Forces are embedded with Afghan special forces on some of their missions, according to NPR Pentagon correspondent Tom Bowman, who spent time with U.S. forces in Afghanistan this past spring.

The Afghan troops have taken the lead role in combat missions and are willing fighters who have absorbed heavy casualties in tough fighting. They've been holding cities and towns across the country, but have struggled to take Taliban strongholds in rural areas, according to the U.S. military and media reports.

But the Taliban's capture of Kunduz last week showed that the Afghan security forces are still vulnerable. This marked the first time the Taliban captured a large city since the U.S.-led coalition drove the Taliban out of power in 2001.

The Taliban took the city by overpowering the police force in Kunduz, a city with some 300,000 residents. The Afghan army arrived soon afterward and dislodged much of the Taliban force within days, according to reports. But some Taliban remnants remained when the Afghan military requested the U.S. airstrike on Saturday.

How Long Will U.S. Troops Stay?

U.S. Gen. John Campbell, the head of the U.S. forces in Afghanistan, told the Senate Armed Services Committee on Tuesday that the airstrike was a mistake and that the U.S. may have violated its own rules of engagement.

Still, in response to questions, he noted that a U.S. Special Operations unit was near the site of the attack, reflecting the level of U.S. involvement in the skies and on the ground.

So what is the future of the U.S. forces in Afghanistan?

Under Obama's timetable, the nearly 10,000 U.S. troops would be reduced to around 5,000 by the end of this year. By the end of next year, most all would be gone except for perhaps 1,000 at the U.S. Embassy in Kabul.

In his remarks Tuesday, Campbell said he has recommended that a larger U.S. military presence remain in Afghanistan beyond 2016.

"The different options that we've laid out through the chain of command provides our senior leaders with options above and beyond the normal embassy presence," Campbell said.

Campbell didn't provide numbers, but Pentagon officials told NPR they range from 3,000 to 5,000 or more. There's also talk of keeping three bases open: Bagram to the north of Kabul, Kandahar in the south and Jalalabad in the east.

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