Afghani President Hamid Karzai, who has led Afghanistan for nearly a decade, said Thursday he would not seek a third term in office in elections due to coincide with the end of NATO combat operations in 2014.
Some political opponents feared that Karzai, who has been Afghanistan's only leader since the 2001 US-led invasion brought down the Taliban, may amend the constitution in order to stay in power.
"The constitution of Afghanistan does not allow anyone to run for the presidency for more than two terms," the president's office quoted Karzai as telling a group of parliamentarians.
He "will not try to run for the presidency for the third time," it said, adding that he was making the announcement in response to "rumours".
With three years to go before Afghanistan's next presidential election, the announcement took many analysts in Kabul by surprise.
On Wednesday, Karzai took a step towards resolving a long-running row over vote-rigging in last September's parliamentary polls by handing authority for adjudicating the issue to the Independent Elections Commission.
But it was not immediately clear whether the two moves were connected.
Karzai has also suffered the loss of a number of key allies in recent months in the midst of a raging Taliban insurgency, notably his powerful brother Ahmed Wali Karzai and the mayor of the southern city of Kandahar, who were both killed in July.
The president, whose initially warm ties with the West have descended into acrimony in recent years, was sworn in as interim leader of Afghanistan in December 2001, shortly after the US-led invasion toppled the Taliban. In 2004, he won the country's first direct presidential ballot with 55.4 per cent of the vote.
But his re-election in 2009 was mired in allegations of corruption, in which challenger Abdullah Abdullah abandoned a second round run-off and investigators threw out a third of Karzai’s original votes because of fraud.
Western diplomats say this was a key factor in deteriorating relations between Karzai and foreign powers, notably the United States.
Afghan analyst Waheed Mujda said he thought Karzai's move was partly motivated by his diminishing power base.
"I believe that even until one year ago, the president had the intention to somehow continue his power, if not as president then as a regional power holder in his birthplace in the south," Mujda said. "But the assassination of his brother and the fact that he seems to have lost credibility among international supporters has left him with no other options."
Another analyst, Mahmood Saikal, cautioned there was no guarantee that Karzai would stick by the pledge.
All of the 140,000 combat troops currently serving in Afghanistan to fight a Taliban-led insurgency, of which 100,000 are from the United States, are due to leave the country by the end of 2014.