KABUL (Reuters) - Pakistan could secure peace in Afghanistan by releasing dozens of senior Taleban prisoners to help kick-start the process, the Afghan foreign ministry said on Saturday, in remarks that underscore the issues vexing peace talks in Qatar.

The ministry's statement was a response to comments by the Pakistani foreign ministry on Tuesday, which welcomed the opening of a Taleban office in the Qatari capital of Doha, saying the country stood "ready to continue to facilitate the (peace) process to achieve lasting peace".

Afghanistan has long accused Pakistan of playing a double game regarding the 12-year-old war against the Taleban, saying its neighbour makes public pronouncements about peace but allows elements of its military complex to play a spoiling role.

"(If) Pakistan has the sincere determination to support the Afghan peace process ... then the most useful and urgent step would be to release those Afghan Taleban leaders who have been arrested by Pakistani authorities," the Afghan foreign ministry said.

"The release of these prominent Taleban leaders would provide the High Peace Council of Afghanistan with the opportunity to start peace talks with them," it added, referring to a body set up by President Hamid Karzai in 2010 to seek a negotiated end to the 12-year war with a Taleban-led insurgency.

The Taleban opened its Doha office this week amid hopeful signs of movement in a long-stalled peace process.

But the opening ceremony caused a stir, with Taleban envoys raising the Taleban flag and signs proclaiming the "Islamic Emirate of Afghanistan", the name used during their brief rule from 1996 to 2001.

This prompted Mr Karzai to cancel plans for an Afghan peace delegation to travel to Qatar and suspend talks with the United States over a vital security pact in the belief it had failed to ensure the Taleban did not misuse the office.

Afghanistan's main opposition party and alliance of the country's northern leaders, the National Front, also condemned the fanfare over the opening of the Taleban office.

"This is an illegal act, in conflict with international conventions and causes serious damage to the legitimacy of the Afghan political state," they said in a statement on Saturday.

Pakistan is seen as crucial to stability in Afghanistan as most foreign combat troops look to leave the country in 2014, given close political and economic ties and because militant sanctuaries straddle the mountainous border.

Afghanistan has long sought the release of, or at least access to, dozens of senior Taleban officials captured in Pakistan who remain in detention there.

Mr Karzai is known to particularly desire the release of Mullah Abdul Ghani Baradar, Taleban leader Mullah Omar's former second in command and a hugely influential figure in the insurgency.

Baradar was the day-to-day commander responsible for leading the Taleban campaign against US and NATO troops, until his capture in 2010 in Karachi by a joint team of US Central Intelligence Agency and Pakistani intelligence officers.

He was also the right-hand man of reclusive Taleban leader Mullah Mohammed Omar, who gave him the nickname Baradar, or brother.

Afghan officials believe Baradar could play a key role in talks with the insurgents, acting as a go-between with Taleban leaders, including Omar.