An Afghan military helicopter crashed on Thursday, killing all 17 on board, officials said, in a blow for a fledgling air force whose resources have been stretched since the withdrawal of most international forces last year.
Afghan troops have been battling a growing insurgency that has killed and wounded thousands of people since the beginning of 2015, with the United Nations putting civilian casualties at almost 5,000 in the first half of the year.
Taliban insurgents claimed their fighters shot down the helicopter, but a government official blamed a technical failure for the crash, just hours after a Taliban suicide bomb attack on an Afghan special forces compound killed six people.
Twelve soldiers and five crew were killed in the crash while the helicopter was ferrying military supplies and troops, said Gul Islam Seyal, a government spokesman in the southern province of Zabul, the site of the crash.
"There were two helicopters," he said. "One of them had a technical problem and contacted the other one and informed the pilot of an emergency landing. As soon as it landed, it caught fire."
The Ministry of Defence confirmed the crash, but said it would release details later.
A Taliban spokesman, Qari Yousef Ahmadi, said on his official Twitter account that the insurgents had shot down the helicopter.
However, there was no enemy fire before the crash, Seyal said. The Taliban often exaggerate battlefield gains.
Afghanistan's military has about 150 aircraft and 390 pilots, just a fraction of the air power of NATO, which flew air support, evacuation and supply sorties before last year's drawdown of troops.
The bulk of the Afghan fleet is made up of aging Mi-17 transport aircraft, but it was not immediately clear what type of helicopter was involved in the crash.
Earlier on Thursday, officials said, a truck bomb targeting an Afghan special forces base in the eastern province of Logar killed three soldiers and three civilians and wounded dozens.
"The bomb was huge and it was carried by a mini-truck," said provincial governor Aleem Fedaee. "It inflicted a lot of damage to the civilians and broke windows even a kilometre away."
The explosion in the provincial capital of Pul-i-Alam, about 100 km (62 miles) from Kabul, wounded more than 20 civilians, including 11 doctors at a nearby hospital, a doctor at the hospital said.
In an email to journalists, Taliban spokesman Zabihullah Mujahid claimed responsibility for the Logar attack.