KABUL: President Hamid Karzai's office brushed off new calls today for Afghanistan's election chief to be sacked ahead of a run-off poll, saying there was no reason for his head to roll over first-round fraud.

Presidential spokesman Humayun Hamidzada said a demand by Karzai's challenger Abdullah Abdullah for Independent Electoral Commission chairman Azizullah Ludin to be replaced had no basis in law and the IEC chief had done "absolutely nothing wrong".

But as Karzai's camp threw its support behind Ludin, a leading international think-tank said the IEC chief and other officials implicated in the fraud on August 20 should be replaced before the November 7 run-off.

"In the remaining days before the second round, IEC chairman Azizullah Ludin should be replaced, and IEC staff and government officials implicated in the fraud should be removed," said the International Crisis Group.

Karzai was forced into a run-off against Abdullah when he fell fractionally short of the 50 percent threshold in the first round, after around a third of his initial tally of votes were disqualified through fraud.

Hamidzada reiterated denials there had been large-scale fraud and said that only the president and not Abdullah could hire or fire the IEC chief.

"I think demands by the candidates -- whether Mr Abdullah or anyone else -- if their demands are based on the laws they can be discussed, accepted, but if their demands are outside the law, obviously the laws are rather important," he told reporters.

"So we'll go for the elections, run-off elections based on the law, the constitution and electoral law." Hamidzada said Karzai agreed to the run-off for the sake of the country even though he believed he won outright.