(Reuters) - The San Francisco 49ers have kept one of the best linebacker units in the NFL intact by signing Ahmad Brooks to a six-year contract extension, the team announced on Tuesday.

The deal, worth $44.5 million according to local reports, will retain Brooks' services on a ferocious defensive unit that includes All-Pro linebackers Patrick Willis and NaVorro Bowman, as well as up-and-coming prospect Aldon Smith.

Brooks became a starter last season and recorded career highs in tackles (59) and sacks (7) while helping the 49ers enjoy a stellar season that took them all the way to the NFC Championship Game.

San Francisco lost in overtime to the New York Giants to fall short of a Super Bowl appearance.

The 28-year-old Brooks was claimed off waivers by the 49ers in 2008.

He showed early but inconsistent promise while setting a franchise record with five forced fumbles by a linebacker in 2009 before emerging last season as a key cog in the San Francisco defense.

(Writing by Jahmal Corner in Los Angeles; Editing by John O'Brien)