JALALABAD, Afghanistan — The Taliban claimed Friday to have shot down a US military transport plane in eastern Afghanistan in a crash that killed 11 people, as the battle for Kunduz raged after the emboldened militants briefly seized the city.

The Taliban's stunning success in Kunduz, their biggest tactical success since 2001, marks a blow for Afghanistan's NATO-trained forces, who have largely been fighting on their own since December.

NATO has not yet confirmed the cause of Friday's crash. The Taliban regularly claim to have shot down military aircraft.

"Our mujahideen have shot down a four-engine US aircraft in Jalalabad," Taliban spokesman Zabihullah Mujahid said on Twitter.

"Based on credible information 15 invading forces and a number of puppet troops were killed."

US Army Col. Brian Tribus said the crash, which occurred at about midnight local time on Friday, left six US soldiers and five civilian contractors dead.

The contractors had been working for "Resolute Support", the NATO-led training mission.

The Taliban claim came as Amnesty International condemned the insurgents' "reign of terror" in Kunduz, which fell to the militants five days ago in a lightning strike.

'Hit list'

A limited picture has emerged of conditions in the city following claim and counter-claim by the Afghan government and the Taliban over who was in control.

However, residents told AFP fierce gun battles and explosions were still echoing in parts of Kunduz late Thursday, and the streets were littered with Taliban bodies and charred and mangled vehicles.

Journalists including an AFP photographer were invited to travel with Afghan troops into the center of Kunduz on Thursday, but after a long wait at a base near the city they were told they had to return to Kabul.

Amnesty International cited civilian testimonies of mass murder, gang rapes and house-to-house searches by militant death squads.

The report, which cited rights activists, claimed militants had a "hit list" and were using young boys to help conduct house-to-house searches to track down their targets, especially women.

Soldiers came under sporadic attacks from insurgents wearing Afghan security uniforms, many of whom took up positions inside residential homes.

Precise losses in the fighting are not known, but so far at least 49 bodies and more than 370 wounded people have been brought to city hospitals, according to health officials.

The wounded included 64 children, medical charity Doctors Without Borders said, adding that its trauma center in Kunduz has been operating "beyond capacity".

Opening gambit?

Jalalabad is situated on a key route from the Pakistani border region — where many militants are based — to Kabul, and it has been the scene of repeated attacks in recent years.

Its airport is home to a major military base, and has come under attack on previous occasions.

In December 2012, Taliban suicide bombers killed at least five people in an hours-long battle at the airport, the third attack on it that year.

The C-130 Hercules is a cargo plane used extensively by the military to ship troops and heavy gear. It can take off and land on rough, dirt strips and is widely used by the US military in hostile areas.

Most NATO combat troops pulled out of Afghanistan last year but a small contingent focused on training and counter-terrorism operations remains, including roughly 10,000 American troops.

The fall of Kunduz showcased the stubborn insurgency's potential to expand beyond its rural strongholds in the south of the country.

Concerns are mounting that the Taliban's success in Kunduz, even if temporary, was merely the opening gambit in a new, bolder strategy.

It is also seen as a game-changer for the fractious militant movement that has been dogged by a leadership crisis since the announcement in July of founder Mullah Omar's death.

Analysts saw it as a boost for new Taliban chief Mullah Mansour, whose recent appointment has been stymied by in-fighting and whose organization has recently been challenged by factions loyal to the Islamic State group.

The renewed energy of the Taliban offensive has also undermined support for President Ashraf Ghani, who has just marked a year in office, and raised questions about Washington's plan to withdraw most US troops from Afghanistan next year.