Free-agent defensive lineman Andre Carter tweeted tonight that he is joining the Patriots.

"I am proud to announce that I will be playing for the New England Patriots for the 2011 season. [Thank] you for your prayers and support," Carter wrote on @mr_carter99, before adding that it was "time to hit the books; on to my playbook."

A Patriots spokesman did not confirm the signing tonight, but a league source indicated there is an agreement with the team and Carter.

The 32-year-old Carter has played for San Francisco (2001-2005) and Washington (2006-2010), having entered the NFL as a first-round draft choice (No. 7 overall pick). At 6-foot-4, 257 pounds, he projects best to defensive end in a more traditional four-man line, in a pass-rushing role.

The Patriots have been utilizing a four-man line through the first stretch of training camp, with Eric Moore and Jermaine Cunningham the top ends. In the last three days, the team has added three new players to the mix -- Mark Anderson, Shaun Ellis and now Carter.

Carter, who has 66 career sacks, totaled 11 in the 2009 season. He has played in 149 career regular-season games, with 133 starts.