KANDAHAR, Afghanistan — At least 17 people, including 12 Afghan army soldiers, were killed Thursday in a helicopter crash in southern Afghanistan, the worst such incident suffered by military forces since the NATO combat mission ended in December.

The Afghan defense ministry said the military helicopter went down due to a technical fault in Shinkay, a district relatively free of insurgent activity in the otherwise volatile province of Zabul.

"The Mi17 transport helicopter crashed, killing 17 people including 12 Afghan army soldiers and five crew members. It was not an insurgent attack, it crashed due to technical difficulties," a senior army commander in southern Afghanistan told AFP on condition of anonymity.

The Taliban claimed they shot down the chopper with a rocket launcher, but the insurgents are known to exaggerate or falsify battlefield claims.

Shinkay district chief Mohammad Qasim Khan also attributed the crash to a technical fault, with another military commander saying an official delegation has been dispatched to the area to investigate the incident.

Aircraft crashes have been a regular risk for Afghan and foreign coalition forces, with troops relying heavily on air transport to traverse Afghanistan's rugged terrain to fight the Taliban.

The insurgents have on occasion brought down NATO helicopters, notably a US Chinook in 2011 which killed 30 Americans, but such incidents have been rare.

In April last year five British troops died when their helicopter crashed in Kandahar province in what London's Ministry of Defence said at the time appeared to be a "tragic accident".

Fledgling Air Force

The fledgling Afghan air force has 83 Mi17 transport helicopters, out of which "a large number are currently under maintenance during the fighting season", said Graeme Smith, a senior analyst with the International Crisis Group in Afghanistan.

"Maintenance is a serious issue for the Afghan Air force and it is hurting their ability to provide air support to ground forces," Smith told AFP.

Afghanistan has a tiny air force compared to NATO's fleet, which carried out supply operations and emergency evacuations until the drawdown of foreign coalition forces last year.

US-led NATO forces ended their combat mission in Afghanistan in December, leaving local forces to battle militants alone, but a 13,000-strong residual force remains for training and counter-terrorism operations.

The Taliban, who were toppled from power in the 2001 US invasion of Afghanistan, have grown bolder as they face Afghan forces directly during their traditional summer offensive launched in late April.

"The Taliban is increasingly using anti-aircraft weapons, posing a risk to Afghan air forces," Smith said.

News of the crash comes after a Taliban suicide truck bomber killed six people early Thursday, in the first major attack since the announcement of leader Mullah Omar's death.

The attack in Pul-i-Alam, the capital of insurgency-prone Logar province just south of Kabul, highlights growing insecurity that is taking a heavy toll on Afghan civilians and security forces.

The bombing coincides with a faltering peace process, with the Taliban confronted by an increasingly bitter power transition after Mullah Akhtar Mansour was announced as the new leader last Friday.

Many of Mansour's rivals have challenging his appointment, exposing the Taliban's biggest leadership crisis in recent years and one that raises the risk of a factional split.

The acrimonious power struggle has cast a pall over a fragile peace process aimed at ending Afghanistan's long war.

The Taliban distanced themselves from the second round of talks with the Afghan government that were scheduled for last Friday but were canceled after the announcement of Omar's death.

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