Republican Sen. Fred Thompson of Tennessee will retire from the Senate at the end of his term, he announced Friday.

"I have decided not to run for re-election. I simply do not have the heart for another six-year term. Serving in the Senate has been a tremendous honor but I feel that I have other priorities that I need to attend to. I hope my friends and supporters who may be disappointed will understand and will believe that I have given them eight good years," Thompson said in a written statement.

Thompson said he will work closely with the president and his colleagues for the remainder of his term, which expires next January. A Republican Senate official said the lawyer and former actor was resigning for personal reasons dealing with his family.

Thompson's daughter, Elizabeth, died Jan. 20 from a brain injury following a heart attack. She was 38.

Though Tennessee has sent increasing numbers of Republicans to Congress in recent years, Thompson's retirement could complicate the party's efforts to regain a Senate majority in the November elections.

Democrats control the chamber by a 50-49 margin; the 100th senator, James Jeffords of Vermont, is an independent who leans Democratic.

Thompson is the fourth Republican to announce his retirement, following Jesse Helms of North Carolina, Strom Thurmond of South Carolina, and Phil Gramm of Texas.

High on the list of Democrats who may try to replace him is Rep. Harold Ford.  Ford, 31, a second-generation lawmaker would become the youngest serving senator.

"As we consider who will fill Senator Thompson’s shoes, I intend to have a conversation on the issues with all Tennesseans, starting in my own congressional district," Ford said. 

Rumors had floated that Thompson would step down in order for Gov. Don Sundquist to appoint former governor, education secretary and presidential candidate Lamar Alexander, to fill the seat, giving Republicans an incumbent edge.

That was shot down, however, when Thompson said he would serve out his term.

Alexander is considered the Republican front runner should he decide to run for the seat, which Republican officials say they are urging him to do. Filing remains open in Tennessee until April 4.

"Former Gov. Lamar Alexander is the Republican Party's strongest candidate to retain the seat," said Scott Reed, a Republican consultant.

The Associated Press contributed to this report.