Pakistan will consider freeing former Afghan Taliban second-in-command, Mullah Abdul Ghani Baradar, if current releases of lower level members help to advance peace efforts, officials from both countries said on Thursday.
"After releasing 13 Taliban, Pakistan promised to free Mullah Baradar if these releases prove effective in peace negotiations," a senior Afghan official close to talks between Islamabad and Kabul told Reuters.
Afghanistan has been pushing Pakistan to release Afghan Taliban captives who could provide leverage in any peace talks with the movement.
Kabul has long been suspicious of its powerful neighbour's intentions. Pakistan has gained credibility in the Afghan peace process by agreeing to release mid-level Taliban over the last two days.
But Pakistan is under growing pressure to free senior Taliban figures such as Baradar to boost reconciliation efforts, as most NATO combat troops prepare to pull out of Afghanistan by the end of 2014 and anxiety grows over the country's security.
Afghan officials believe he may command enough respect to persuade the Taliban to engage in talks with the Kabul government.
Asked if Baradar would also be freed, a senior Pakistani foreign ministry official said that was possible if the release of the Taliban figures "produced results".
"We've released about a dozen mid-level Taliban commanders now. The impact of this on reconciliation efforts and the peace process will determine the number and pace of future releases, as well as releases of high-level prisoners."
In August, senior officials from both countries said Afghan delegates held secret talks with Baradar, who was caught in the Pakistani city of Karachi in 2010.
The Afghan government believes Baradar is more open to dialogue than many of his comrades. It is not entirely clear whether Baradar would promote peace or war against President Hamid Karzai's Western-backed government if he returns home.
As military chief of the Taliban, he supervised ambushes and roadside bombings that proved highly effective against some of the world's most powerful armies. But he was also known as a leader that could secure compromises.
In the months before his arrest, Baradar authorised contacts with United Nations representatives to explore the possibility of dialogue, former U.N. and Taliban members said.
Afghan officials have often viewed Pakistan as a reluctant partner in its attempts to broker talks with the Taliban.
They believe Pakistan is holding Baradar and other senior Taliban figures to influence any settlement of the Afghan war now in its 11th year.
Afghans fear failure to secure a peace deal before 2014 could trigger a civil war, or give the Taliban a chance to seize power again.
A senior Afghan official told Reuters last week that no breakthrough was expected anytime soon. The Taliban said in March they were suspending separate peace talks with the United States held in Qatar because of "vague" U.S. statements.
Pakistan joined the U.S. war on militancy after the September 11 hijacked plane attacks in 2001.
But U.S. officials accuse it of using Afghan insurgent groups such as the Taliban and the Haqqani network as proxies to counter the influence of India in Afghanistan.Pakistan denies the allegations and says it has sacrificed more than any other country in the fight against militancy.