KABUL: Afghanistan prepared Monday to roll out partial results from a hotly contested election marred by allegations of massive fraud, with President Hamid Karzai and his chief rival both claiming the lead.

Officials say they will release the first results from Tuesday, but warn that the final outcome could be affected by investigations into the claimed abuses.

Karzai had been tipped to ease to a second term, but a strong campaign from former foreign minister Abdullah Abdullah and reports of miserable turnout in the president's southern powerbase have boosted speculation of a run-off vote.

But while Abdullah on Sunday alleged widespread rigging in favour of Karzai, some observers said he could be positioning himself for defeat and for a role in the political opposition.

"Negotiations are well under way for Abdullah to accept defeat at the first round. It may depend on what he gets in exchange," one Western diplomat in Kabul told AFP on condition of anonymity.

Diplomats expect Abdullah to demand a far higher price than Mohammad Younis Qanouni, who was runner-up to Karzai at the first presidential election in 2004 and who went on to become speaker of the national assembly.

"Abdullah can ask for more. The first results to be unveiled by the Independent Election Commission (IEC) on Tuesday can impact the result of these negotiations," said the diplomat.

With Western allies committed to putting Afghanistan on the path to democracy, they would likely court Abdullah, who might look forward to another bid for the presidency in the future.

Most analysts believe a second round would deal Abdullah a humiliating defeat because Karzai has a broader base of support from the Pashtun community, but said it was unclear whether he was willing to take the risk or not.

A spokesman for Abdullah, who campaigned to introduce a more parliamentary system of government, left the door open to him becoming Afghanistan's first serious post-Taliban opposition leader.

"It's too early to talk about this but in general whether he wins or doesn't win, Dr Abdullah remains committed to his principles and goals," the spokesman, Sayed Aqa Fazil Sancharaki, told AFP.

"This is to bring change -- to amend the constitution, to change the system from presidency to parliamentary, and elected governors," he added.

Western backers of Karzai's government have urged presidential candidates to refrain from premature announcements, respect the electoral process and for their supporters to keep calm.

"The president is awaiting the results, the final results from the IEC," Karzai spokesman Hamid Elmi told AFP, refusing to be drawn on whether overtures had been made to tie Abdullah into a future Karzai administration.

Analysts point to possible difficulties in a definitive result being delayed by investigations into irregularities. The Electoral Complaints Commission said Sunday that 225 complaints had been lodged so far.

"The Karzai camp says they have 70 percent of the vote. We have to wait and see in the coming days. It'll be problematic if the results drag out," said Haroun Mir, from Afghanistan's Centre for Research and Policy Studies.

Abdullah's powerbase in the north means he has the widespread support of Tajiks, whereas Karzai's strong influence in the Pashtun-dominated south means the two largest ethnic groups in Afghanistan are potentially divided.

Turnout appears to be the highest in the northern province of Balkh and the wealthy western province of Herat, but paltry in southern areas where the Taliban hold sway.