Presidential wave: Hamid Karzai prepares to greet Ban Ki-Moon, UN secretary-general, in Kabul on Monday after he was declared re-elected

Hamid Karzai was declared the winner of Afghanistan’s presidential elections on Monday, ending a political crisis sparked by evidence of widespread vote fraud but leaving doubts over the government’s legitimacy.

Western powers congratulated Mr Karzai, relieved to see an outcome after wrangling that has delayed a decision by Barack Obama, the US president, on whether to send more troops to Afghanistan to fight the Taliban.

Mr Karzai and his allies now face the difficult tasks of repairing relations strained by attempts to rig the polls in his favour and overcoming fears that the administration will lack the credibility to support a new counter-insurgency strategy designed to rescue the west’s war effort.

Election officials said they had decided to hand Mr Karzai another five-year term after Abdullah Abdullah, his key rival, withdrew from a run-off that had been due to take place on Saturday. Mr Abdullah said the vote would lack credibility.

“His excellency Hamid Karzai, who has won the majority of votes in the first round and is the only candidate for the second round, is declared by the Independent Election Commission as the elected president of Afghanistan,” Azizullah Lodin, chairman of the IEC, said in Kabul.

Ban Ki-moon, the UN secretary-general, who was visiting Kabul less than a week after a Taliban attack left five UN workers dead in the Afghan capital, welcomed the decision.

A UK government spokesman said Gordon Brown, the prime minister, had contacted Mr Karzai to congratulate him on his re-election. “They discussed the importance of the president moving quickly to set out a unifying programme for the future of Afghanistan”, the spokesman said.

The cancellation of a second round of voting – which would have taken place with only one candidate and risked a repeat of the Taliban attacks, fraud and low turnout that marred the election on August 20 – came as a relief to western powers and many Afghans.

In depth: Afghan elections

Follow the developments in the run-off election scheduled for November 7 with news and analysis from FT reporters

Mr Karzai’s critics said the elections have damaged Afghanistan’s attempts to build a democracy. “The announcement that was made by the electoral commission today will not solve the problems of Afghanistan and it doesn’t have any basis in law,” said Fazel Sancharaki, a spokesman for Mr Abdullah’s campaign. Mr Abdullah has yet to respond.

The outcome followed weeks of electoral drama marked first by revelations of ballot rigging and a tense showdown between western powers and Mr Karzai, who rejected the findings of UN-backed fraud investigators who struck out almost a third of his votes.

He accepted the need for a run-off only after international pressure. Afghan analysts believe Mr Karzai will reach out to Mr Abdullah’s camp to create a government that will reflect a regional and ethnic mix. “I wouldn’t expect myself to see Abdullah in the cabinet,” said a senior western diplomat. “I think there will be a role for Abdullah of some kind but probably outside government and the details of that will have to be worked out.”

Later on Tuesday Mr Karzai is expected to give a victory speech or declaration in Kabul where he will set out his reaction to the election, talk about his agenda. Inauguration would follow in the next few weeks where western officials say foreign ministers may gather to offer some endorsement to the government.

One senior western government official said he had told the Afghans that if they put “a political dead beat into a ministerial job where we are putting a significant amount of money, then that money will stop”.