Republican candidate Fred Thompson has announced he is quitting his bid for the U.S. presidency.

The television actor and former senator from Tennessee said in a statement Tuesday that he has withdrawn his candidacy.  He did not say if he would endorse any of his rivals.

Thompson entered the contest with high expectations that his television career and Republican establishment credentials would propel him to an early lead.

But he failed to finish higher than third in any of the contests to choose the Republican presidential nominee.  On Saturday, he finished third in South Carolina, which he had said he needed to win.

Meanwhile, Illinois Senator Barack Obama and New York Senator Hillary Clinton are back campaigning in the close race for the Democratic presidential nomination, a day after clashing in a televised debate.

Obama holds a small lead over Clinton in South Carolina, which has the next Democratic Party primary in the state-by-state nomination process.  Black voters in the state are expected to account for more than half of the vote tally, and their support for Obama is expected to be a key factor in Saturday's poll.

In a heated debate Monday, the two traded accusations about their record as lawyers. Obama also said former President Bill Clinton, an important figure in the Democratic party and Senator Clinton's husband, was misrepresenting Obama's record as a legislator.

Republican Party candidates are holding events in Florida ahead of their party's next primary on January 29.

The contenders from both parties are hoping to build momentum before the critical primaries and caucuses on so-called Super Tuesday, February 5 when 22 states hold presidential nominating contests.

Some information for this report was provided by AFP, AP and Reuters.