Taliban fighters are believed to have captured all passengers and crew of a Pakistani government helicopter that crash-landed in eastern Afghanistan.

Afghan officials said the helicopter went down late on Thursday in Logar province, close to the Afghan-Pakistan border, an increasingly lawless area since a two-year Pakistani military operation pushed many Taliban and allied fighters further into Afghanistan.

"The chopper was not shot but made the landing because of technical failure," Sameem Saleh, spokesman for Logar's governor, told Reuters news agency.

"Those detained by the Taliban are Pakistanis."

Nafees Zakaria, a spokesman for the Pakistani foreign office, confirmed that a helicopter belonging to the Punjab provincial government had gone down in Logar, but said the fate of those on board was not yet clear.

"The Afghan authorities have assured they will investigate and learn the whereabouts of the helicopter and the passengers," he said.

Zakaria said that seven passengers were on board, six of them Pakistanis and one a Russian technician. The pilot was Pakistani.

The Russian-made MI-17 transport helicopter had permission to fly over Afghan airspace on its way to Uzbekistan further north, he said.

A senior Pakistani military official also said the helicopter was en route from Peshawar in northwest Pakistan to Uzbekistan for maintenance when it experienced technical failure and made an emergency landing.

The crash came a few hours after a van carrying 12 tourists from the UK, US and Germany was attacked in the Chesht-e-Sharif district of Herat province in western Afghanistan.

The Taliban claimed responsibility for the attack, which wounded at least seven people. In a statement, Qari Yousef Ahmadi, Taliban spokesman, said the foreigners were killed - a claim Afghan officials denied.

Pentagon decision

In a separate development, the US has withheld $300m in military assistance to Pakistan after the Pentagon concluded that the country was not taking adequate action against the Haqqani network, a Pakistan-based armed group aligned with the Taliban.

Relations between US and Pakistan have been frayed over the past decade, with officials in the US frustrated by what they term Pakistan's unwillingness to act against armed groups such as the Afghan Taliban and the Haqqani network.

Pakistan rejects harbouring fighters but says there are limits to how much it can do as it is already fighting multiple armed groups and is wary of a "blowback" in the form of more attacks on its soil.

OPINION: US must challenge Pakistan's duplicity on Afghanistan

The $300m was not released because Ashton Carter, the US secretary of defense, decided against making a certification "that Pakistan has taken sufficient action against the Haqqani network", Adam Stump, Pentagon spokesman, said on Wednesday.

Pakistan is the largest recipient of the Coalition Support Fund (CSF), a US government programme to reimburse allies that have incurred costs in supporting operations against armed groups.

According to Pentagon data, about $14bn has already been paid to Pakistan under the CSF since 2002.