The Taliban have offered a three-month ceasefire in exchange for the release of 7,000 insurgent prisoners, an Afghan government negotiator said yesterday, as Pakistan confirmed the militant group had control of a key border crossing.

"It is a big demand," said Nader Nadery, a key member of the government team involved in peace talks with the Taliban, adding the insurgents also demanded the removal of their leaders' names from a United Nations blacklist.

It was not immediately clear how the government would react to the ceasefire offer, or how new it was, and it comes as the United States accelerates the pace of a troop withdrawal due to be finished by August 31.

A spokesman for the Taliban, whose leaders are scattered across the region, said he was only aware of the suggestion of a ceasefire over the forthcoming Eid al-Adha holiday.

Nadery's revelation came as Pakistan security forces used tear gas yesterday to disperse hundreds of people who tried to force their way across the border from Chaman to Spin Boldak in Afghanistan.

Yesterday, Pakistan's foreign ministry confirmed the border crossing was in the hands of the Taliban.

"They have taken control of Spin Boldak border crossing," said ministry spokesman Zahid Hafeez Chaudhri, a day after the Taliban seized the town.

The border was closed Wednesday by Pakistan officials after the Taliban seized Spin Boldak and raised insurgent flags above the town.

"An unruly mob of about 400 people tried to cross the gate forcefully. They threw stones, which forced us to use tear gas," said a security official on the Pakistan side.

He said around 1,500 people had gathered at the border Wednesday waiting to cross.

Jumadad Khan, a senior government official in Chaman, said the situation was now "under control".

An Afghan Taliban source told AFP that hundreds of people had also gathered on the Afghan side, hoping to travel in the other direction.

Later yesterday, a Pakistani border official told AFP that the border would open today.

The crossing provides direct access to Pakistan's Balochistan province -- where the Taliban's top leadership has been based for decades -- along with an unknown number of reserve fighters who regularly enter Afghanistan to help bolster their ranks. 

Muska Dastageer, a lecturer at the American University of Afghanistan, said the Taliban ceasefire offer was a likely attempt by them to consolidate the positions they have gained so swiftly in recent weeks.