Chair of ECC Grant Kippen: "We've found fraud irregularities around the country"
A panel probing fraud claims in the Afghan election has found Hamid Karzai did not gain enough valid votes for an outright win, the BBC understands.
Preliminary results from August's first round had placed Mr Karzai comfortably over the 50% plus one vote threshold needed to avoid a run-off.
But one poll monitoring group estimates that almost one million of Mr Karzai's votes have now been deemed invalid.
Poll rules say Mr Karzai must now face a run-off against his nearest rival.
In Washington, the US Secretary of State Hillary Clinton said she expected Mr Karzai to announce on Tuesday how he would "set the stage" to resolve the country's political crisis.
"I am very hopeful that we will see a resolution in line with the constitutional order in the next several days," Mrs Clinton said.
Lyse Doucet, BBC News, Kabul
When this tangled process began, the ECC, the only electoral body composed of Afghan and foreign representation, was regarded as the "final arbiter".
The IEC's role was to ratify and announce the results. The IEC is accused by many of being too close to a president who appointed all its commissioners. It now says it needs "a day or two" to examine the details of the ECC report.
One source warned of a possible "train crash". Others are still hoping a compromise can emerge at this critical 11th hour.
President Karzai has repeatedly warned foreign countries not to interfere in the election process.
Sources say he firmly believes Western countries, in particular the United States and Britain, are conspiring to rob him of victory.
Although there has been no official reaction from Mr Karzai to the vote probe, he told the UN secretary general he would "fully respect the constitutional order", according to a UN spokeswoman quoted by AFP.
The BBC's Martin Patience in Kabul says the Afghan leader believes an election victory has been stolen from him and he is threatening to block attempts to hold any second round.
But Washington - which has been debating a request for 40,000 more US troops to be sent to Afghanistan - warned at the weekend no more soldiers would be deployed until a political resolution was reached.
A spokesman for the UN in Afghanistan, Aleem Siddique, said on Monday they now expected the IEC to "swiftly" announce either final results or a runoff.
AFGHAN ELECTION BODIES
Constitutional body appointed by Afghan president to oversee polls
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