NATO chief Anders Fogh Rasmussen called on the Afghan government Monday to ensure free and fair presidential elections next year after widespread allegations of fraud marred the 2009 poll.
The credibility of the vote is seen as crucial to avoiding an escalation of violence as NATO combat troops withdraw next year, leaving Afghan soldiers and police to tackle the Taliban insurgency.
"It will be vital that these elections are inclusive, and that the process and the outcome are acceptable to the Afghan people," said NATO Secretary General Rasmussen warned during a previously unannounced visit to Kabul.
President Hamid Karzai, who has been the head of state since the 2001 US-led invasion brought down the hardline Taliban regime, is constitutionally barred from running for a third term.
There are no clear front-runners in the election, which is due in April 2014, though reports have suggested that some of Karzai's relatives could stand.
Karzai has repeatedly said he will not interfere in the polls and only wants a peaceful handover of power.
International concern over the election grew late last year when the government moved to scrap a UN-backed watchdog in favour of a tribunal that could give Karzai more control over polls.
The decision to scrap the Electoral Complaints Commission (ECC) has yet to be approved by parliament but was passed by the council of ministers.
The replacement tribunal would be appointed by the Supreme Court, whose judges are in turn appointed by the president and endorsed by parliament.
In 2009, the ECC investigated thousands of complaints in the presidential election, most of them related to alleged ballot rigging by Karzai's supporters.
The watchdog ordered ballots from 210 polling stations to be disqualified in a probe that ultimately forced Karzai to accept a second-round run-off, until it was abandoned when his opponent pulled out.
Rasmussen also called for Afghanistan to make more progress fighting corruption, boosting women's rights and strengthening the rule of law.
"That will be key to maintain stability within Afghanistan, and support within the international community," he said.