Afghanistan's security chiefs have been ordered to make emergency preparations for a second round of voting, in the clearest sign yet that Hamid Karzai will admit he didn't win August's fraud-ridden presidential poll.

Hamid Karzai has come under intense pressure from world leaders over the last few days. (SHAH MARAI/AFP/Getty Images) Senior Afghan officials at the Ministry of Interior in Kabul said the president had authorised preparations for a second round.

Karzai had threatened to ignore the findings of a UN-backed watchdog which ruled that almost a third of his three million votes were fraudulent, and he banned the Ministry of Interior from liaising with defence chiefs to plan security for a run-off.

But a police general at the ministry told The Times that they received permission from the palace earlier today.

Afghan law requires a run-off within two weeks of the certified result, if none of the candidates secure more than 50 per cent of the vote.

Preliminary results gave Karzai 55 per cent, but the Electoral Complaints Commission slashed his tally to 48 after investigating thousands of reports of "state-sponsored" fraud.

The President's spokesman said this morning that he would abide by the decision of the Independent Electoral Commission (IEC), which is due to be announced later today.

As a result, by the end of the day Afghans will at long last have a clear indication of the official outcome of August's election.

Mr Karzai is due to make his position clearer during a nationwide address this morning, flanked by the US Senator John Kerry, and Kai Eide, the UN representative in Afghanistan. Sources said that he was was prepared to make concessions, either agreeing to a run-off in a month's time or forming a coalition with his closest rivals.

The final announcement by the IEC is set to follow within hours.

Today's developments come after a tense weekend when the President seemed inclined to brazen it out and insist that he had won a clear majority in the first round, declaring the evidence of massive voting fraud to be "totally fabricated".

Frantic diplomatic negotiations are understood to have taken place behind the scenes, with both Mr Kerry and the French Foreign Minister, Bernard Kouchner, in Kabul seeking to persuade Mr Karzai either to accept a deal with his main opponent or to put his name forward again in a second round of voting.

Last night Mr Kerry attended a late meeting at the presidential palace along with the British and French ambassadors and Mr Eide, where a deal was understood to have been struck that will enable world leaders to applaud Mr Karzai as a "statesman".

One diplomatic source said that Mr Karzai had been persuaded by blunt ultimatums from the US, Britain and the UN that if he refused to back down he would be cut adrift. Gordon Brown is one of a number of world leaders who has rung Mr Karzai in the last few hours to pressure him.

A two-month investigation by the country's UN-backed Electoral Complaints Commission has found "clear and convincing evidence of fraud".

The complaints commission submitted its final report to the election commission yesterday. Until now the government-appointed IEC has appeared to side with Mr Karzai, refusing to accept the complaints commission's preliminary findings.

"Our commissioners are meeting now to discuss the figures sent by the ECC and will announce a final decision today," Noor Mohammad Noor, the Independent Election Commission spokesman, said this morning.

The ECC has declined to publish its final figures, but senior officials in the investigation confirmed a report by Democracy International, an advocacy group, which showed that Mr Karzai's vote fell from 3.1 to 2.1 million after the investigation.

The Afghan Constitution requires the winner to capture more than 50 per cent of the vote in the first round. One election observer said yesterday: "There's just no way Karzai got the 50 per cent plus one vote to win."

The ECC tally has increased the share of his closest rival, the former Foreign Minister Dr Abdullah Abdullah, from 28 to 32 per cent - though he too had more than 200,000 ballots discounted. Overall, around 1.26 million recorded votes were excluded from an election that cost the international community more than $300 million (£183 million).

A second round of voting would almost certainly be won by Mr Karzai, though there is no guarantee that it would be conducted more fairly than the first, and the onset of winter means that much of the country will soon be inaccessible because of snow.

President Obama has been delaying a decision on whether to agree the troop surge requested by his top Afghan general until greater clarity emerged on whether Afghanistan had a legitimate and credible government that the US could work with.

Robert Gibbs, Mr Obama's spokesman, said: "It has been obvious to the world that allegations of fraud had to be investigated." He added that it was now "incredibly important for the world to see that Afghan leaders are willing to make this process legitimate".

Hillary Clinton, the US Secretary of State, hinted last night that the US had finally had the assurances they needed from Mr Karzai, saying: "He is going to announce his intentions. I am going to let him do that, but I am encouraged at the direction that the situation is moving. I am very hopeful that we will see a resolution in line with the constitutional order."