Global pressure mounted on President Hamid Karzai on Sunday to accept a possible runoff in Afghanistan's disputed election as extended diplomacy delayed the announcement of official results from the August poll, Reuters reported.

The row stemming from the election, marred by allegations of mass fraud, is a setback for the United States as President Barack Obama considers whether to send more troops to Afghanistan to fight a resurgent Taliban.

In Kabul, diplomats and observers said Karzai's supporters resisted accepting the findings of an inquiry by the U.N.-backed Electoral Complaints Commission into poll fraud -- a key factor behind delays in the announcing the outcome.

"They are putting up resistance," said one official familiar with the discussions. "Legally it is difficult to see on what grounds they can reject any of the findings."

Under Afghan law, Afghanistan's independent election commission has to accept ECC probe findings, adjust the election tally and announce the final result.

As talks proceeded, observers said pressure was mounting on Karzai to agree to face his main challenger, former Foreign Minister Abdullah Abdullah, in a second round, or form a power-sharing government.

The Afghan leader has made clear he would prefer not to fight a second round and has spoken out against the investigation, making veiled accusations of foreign meddling.

Global leaders have spoken to Karzai over the past two days, including U.S. Secretary of State Hillary Clinton.

A host of high profile visitors have been in Kabul for the weekend, including U.S. Senate Foreign Relations Committee Chairman John Kerry and French Foreign Minister Bernard Kouchner.

Kerry said Washington should not proceed with a new Afghan strategy without a clear partner in Kabul.

If enough votes are thrown out from Karzai's tally he will face Abdullah in a second round within two weeks of the result -- already a tough task due to the rapid onset of winter in the mountainous nation as well as security concerns.

Preliminary figures gave Karzai 54.6 percent of the vote and Abdullah 28 percent.

While accusing Karzai's camp of fraud and calling for a second round, Abdullah has hinted he might be open to discussions after the first round result is announced.

The election is a vital element in Western plans to stabilize Afghanistan and deny sanctuary there to militants believed to have used it as a base for actions across the globe, including the September 11, 2001, attacks on the United States.

More than 100,000 foreign troops are in Afghanistan fighting Taliban insurgents, but growing casualties and doubts about the Karzai government are undermining support for the effort in the United States, Britain and other countries involved.