KABUL - Afghanistan's election fraud watchdog said on Sunday it is probing 567 allegations of abuse it considers serious enough to affect the outcome of the Aug 20 vote, more than double the number announced two days ago.

The country has been in a state of political limbo since the presidential election, with partial results so far placing President Hamid Karzai in the lead, but not by enough to avoid a second round against his main challenger, Abdullah Abdullah.

The election, which Taliban militants failed to scupper despite scores of rocket attacks, was initially hailed as a success by Western officials, but those assessments have grown more circumspect as accusations of fraud have mounted.

The latest partial preliminary results, released late on Saturday, gave Karzai 46.3 percent of the vote to 31.4 percent for Abdullah, with 35 percent of polling stations tallied.

Most votes have yet to be counted in the south, heartland of Karzai's ethnic Pashtun support -- and also the area where Taliban violence and threats had their greatest impact on turnout, and where complaints of fraud are concentrated.

Abdullah, a former foreign minister, has accused the president's camp of stuffing ballot boxes on a massive scale, and says he will not accept the outcome if cheating was decisive.

An Electoral Complaints Commission, with foreign members appointed by the United Nations, can discard results from entire polling stations if it suspects abuse.

Ahmad Muslim Khuram, spokesman for the body, said it was now looking into 2,493 complaints, including 567 it classifies as Category A, meaning they are serious enough to alter the outcome. On Friday there were 270 Category A complaints.

To avoid a run-off, a candidate must win more than 50 percent of the vote. The results from southern provinces might put Karzai over the top, but could be challenged by the complaints body.

Full preliminary results are due later this week, with the final result, after all complaints are checked, due two weeks later. A run-off, if needed, would be held in October.

(Editing by Nick Macfie)

Afghanistan