"I tell everybody, just take a deep breath and relax. We can't predict what the results are going to be," Blackwell, the state's top election official, told CNN television.

Blackwell said that under state law, Ohio election officials would begin counting so-called provisional ballots 11 days from Tuesday on November 13.

Voters are allowed to cast a provisional ballot if there is any doubt that they are valid registered voters. Officials will spend ten days determining whether the ballots are valid, and then those will be counted on November 13.

Ohio also counts absentee ballots so long as they are postmarked by November 2 and arrive within the 10-day grace period.

Military members serving overseas

Many absentee ballots have been cast by military members serving overseas, Blackwell said.

"We're not going to start counting those ballots until the 11th day after the election," Blackwell said.

Two television networks have said President George W. Bush has won Ohio. But Senator John Kerry's campaign has refused to concede defeat saying that there are still 250 000 votes to be counted.

Victory in Ohio would put the Republican president on the verge of re-election.

"The vote count in Ohio has not been completed. There are more than 250 000 remaining votes to be counted. We believe when they are, John Kerry will win Ohio," said Kerry campaign manager Mary Beth Cahill in a statement.

"It could be 250 000 as the Democrats are claiming...we have a system that can deal with an honest count and an honest process regardless of the margin," Blackwell said.