Kerry landed in the Afghan capital on Thursday for meetings with presidential contenders Ashraf Ghani and Abdullah Abdullah as well as outgoing President Hamid Karzai.

Kerry’s visit comes amid allegations of fraud in Afghanistan's June election, tipping the country into a political crisis, with the United Nations voicing fears that the contested outcome could revive the ethnic unrest in the country during the 1990s.

Kerry negotiated a deal with the two rivals last month in which they reportedly agreed to a complete an audit of the eight million votes, and for the winner to form a national unity government.

However, the deal has made little progress due to further disagreements between them, and no date has yet been set for the delayed presidential inauguration.

The clock is now ticking for a new president to be in office before the end of this month ahead of a NATO summit on September 4-5, when member states will decide on future finance and support for the war-torn country.

"We would like to see the inauguration ideally by the end of the month," said an unnamed US official travelling with Kerry as cited in wire reports.

"It's important for a new president to be able to go to NATO and ask for these commitments, including continued Afghan National Security Forces costs,” he reportedly added.

The development comes just days after a US major general was killed in Afghanistan by a man in Afghan army uniform.

As usual, Kerry's visit to Kabul was not announced before he landed for security reasons.

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