Chuck Hagel won't seek a third term in the Senate, FOX News confirmed Saturday.

The Nebraska Republican will announce his retirement on Monday at a press conference. Hagel informed Senate Minority Leader Mitch McConnell of his decision on Friday.

A decorated Vietnam veteran, Hagel, 60, has earned national recognition as one of the most vocal GOP critics of President Bush’s Iraq policy. Early this year, Hagel labeled Bush’s troop build-up in Iraq as "the worst foreign policy blunder since Vietnam — if it's carried out."

Several Republicans, including former Nebraska governor and current U.S. Secretary of Agriculture Mike Johanns, have been mentioned as possible candidates for Hagel’s Senate seat, according to the World-Herald.

A Republican official also said Hagel won't run for the White House in 2008.

The decision by Hagel is the latest in a string of setbacks for minority Republicans in the Senate, who must defend 22 of the 34 seats on the ballot next fall.

Last week, Sen. John Warner of Virginia announced his retirement, a decision expected to create an intensely competitive race for a seat he probably would have held easily had he decided to run again.

The Associated Press contributed to this report.