From his home town of Boston, Massachusetts, US senator Kerry expressed his congratulations to Bush, telling the Republican president the country now was too divided.

"Congratulations, Mr. President ... We really have to do something about it," Kerry said in the telephone call described by sources as lasting less than five minutes, media reported.

Bush agreed, calling Kerry a worthy, tough and honorable opponent, according to the report.

Kerry's call came after his campaign learned that Bush was assured of victory in key battleground state of Ohio, giving the president an unquestioned majority in the Electoral votes.

Both Bush and Kerry will make a statement later in the day about the election, according to US TV networks. Kerry's speech is scheduled at 1 pm EST and Bush will deliver a statement at 3 pm EST.

Earlier in the day, White House Chief of Staff Andrew Card said Bush will hold off a formal victory declaration to give Kerry the "time to reflect" on the results.

Meanwhile, the Kerry camp made an announcement, refusing to concede defeat before every vote in the controversial state of Ohio had been counted. "We will fight for every vote," Senator John Edwards, Kerry's running mate told supporters in Boston.

"We've waited four years for this victory. We can wait one morenight," he said.

At earlier hours on Wednesday, Fox and NBC, two major television networks, projected that Bush had won the 20 electoral votes in the critical state. But three other major TV networks said the result was too close to call there as count went on.

Kerry refused to concede defeat in the crucial state of Ohio, which carries 20 electoral votes.

"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.

Kerry won 19 states and the District of Columbia and 252 votes while Bush won 29 states and 274 votes.

According to the country's election system, Americans do not directly choose the president. Instead, after ballots are counted in each state, state representatives, called electors, will vote on the basis of the state tallies in an Electoral College, a system which has been operating since 1788.

There are altogether 538 electors and a minimum of 270 electoral votes is necessary to win the Electoral College.