SOMERVILLE, Mass. (AP) – Gov. Deval Patrick has formally endorsed Democratic U.S. Senate candidate Elizabeth Warren.

Patrick met on Wednesday with a couple hundred Warren campaign volunteers at her Somerville headquarters.

The meeting and endorsement comes days before the Democratic state convention in Springfield on Saturday.

Patrick urged the volunteers to step up their canvassing on behalf of Warren, the most likely Democrat to take on Republican incumbent Scott Brown in November.

But Warren could face a primary challenge from Marisa DeFranco, an immigration attorney from Middleton, who needs support from 15 percent of the convention delegates to win a spot on the September primary ballot.

Copyright 2012 The Associated Press.