ISLAMABAD - Pakistan told Afghanistan on Friday it was "preposterous" to think Islamabad could deliver the Taliban's leader to the negotiating table and warned the neighbouring nation against "ridiculous" expectations about peace talks.

The public comments by Pakistan's Foreign Minister Hina Rabbani Khar were an unusually harsh upbraiding for the diplomatic world, where such quarrels usually play out behind closed doors. They reflected Pakistan's anger at repeated allegations by Afghanistan and the U.S. that it is harbouring the Taliban's leadership on its territory.

Khar spoke following talks between Pakistan and Afghanistan in Islamabad that were supposed to identify specific steps Pakistan would take to facilitate peace negotiations, but ended in apparent acrimony.

It was a serious setback for a peace process that the United States is strongly promoting as a way to end the decade-old Afghan conflict and allow it to withdraw most of its combat troops by 2014 without the country further descending into chaos.

The foreign minister said Pakistan supports an Afghan-led peace process but cautioned against Kabul expecting too much in terms of Islamabad's ability to provide them access to the Taliban's leaders.

"If you have unrealistic, almost ridiculous expectations, then you don't have common ground to begin with," said Khar.

Pakistan is seen as key to the process because much of the Taliban leadership, including chief Mullah Omar, is believed to be based in the country, and the government has historical ties with the group. Analysts say Pakistan can either help the talks or act as a spoiler.

But Islamabad has always denied Taliban leaders are using its territory and rejected allegations that the Pakistani government has maintained its links to the group, frustrating Afghan and American officials who say Pakistan is not aggressively going after the terror group.

It's unclear whether Karzai asked Pakistan for help getting to Omar during his current visit to Islamabad, and he made no public mention of the cleric. But he has called on Pakistan to facilitate contact with Omar and other Taliban leaders in the past.

The presidents of Afghanistan, Pakistan and Iran held a three-way summit in Islamabad over the past two days that focused on Taliban peace talks and other regional issues. Pakistan and Afghanistan also held bilateral meetings on the side of the summit, which ended Friday.

The Pakistani foreign minister indicated her government was still uncertain on exactly what role Afghanistan wanted Islamabad to play in the peace negotiations, saying "they have not conveyed that clarity to us."

In the past, Afghan officials have said they want Islamabad to offer tangible assistance, such as giving Taliban representatives safe passage to meeting sites outside of Pakistan. Afghan officials have also said that they want Islamabad to grant access to Mullah Abdul Ghani Baradar, a top-ranking Taliban official who was captured in Pakistan in 2010. His arrest reportedly angered Karzai because Baradar had been in secret talks with the Afghan government.

The Afghan president has said he has been seeking Pakistan's help in the peace process for some time, but that so far, it has not provided much more than words of support.

"What we need now is to formulate a policy that is actionable and implementable, and actually act upon it," Karzai said at a press conference Friday featuring Pakistani President Asif Ali Zardari and Iranian President Mahmoud Ahmadinejad. The Pakistani foreign minister's comments came as she spoke to reporters after the news conference.

Khar said that any expectation that Pakistan can deliver the Taliban's chief for talks is "not only unrealistic, but preposterous."

Asked about reports that the most recent discussions between Afghanistan President Hamid Karzai and Pakistani officials were confrontational, Khar said, "The talks were very, very useful, and if they are hard, that is fine."

"We need to have some hard talks," she said.

Many analysts believe Pakistan has maintained links with the Taliban because it is seen as a key ally in Afghanistan after foreign forces withdraw, especially in countering the influence of Islamabad's neighbour and archenemy, India. Pakistan helped the Taliban seize power in Afghanistan in the 1990s.

That history has contributed to the tense relationship between Afghanistan and Pakistan. Ties were strained further last year when a suicide bomber assassinated former Afghan President Burhanuddin Rabbani in Kabul. He had been serving as Afghanistan's envoy to Taliban peace talks, and Afghan officials accused Pakistan of playing a role in the killing -- allegations it denied.

There have been some signs that momentum for Taliban peace talks has been growing.

The Taliban are setting up an office in the tiny Gulf state of Qatar in the first step toward formal negotiations. Also, the Obama administration is considering releasing five top Taliban leaders from the U.S. detention centre in Guantanamo Bay as a starting point for talks.

But the process has also been riddled with rumour and uncertainty.

Karzai initially resisted the U.S.-backed move by the Taliban to set up a political office in Qatar because he felt the Afghan government had been sidelined and not kept fully apprised of the process of getting an office established. He said he preferred Saudi Arabia, and members of the Afghan government's peace council have said that while the political office might be in Qatar, actual talks could take place in Saudi Arabia or another location.

Tension between Pakistan and the U.S. has also complicated the process, especially following American airstrikes in November that accidentally killed 24 Pakistani troops at two Afghan border posts.