Rep. Ed Markey (D-Mass.) is set to announce his endorsement of Rep. Michael Capuano (D-Mass.) in the race for Ted Kennedy's Senate seat.

Markey, who is known as the dean of the state's congressional delegation, becomes the seventh member of the state's delegation to back Capuano, who also landed the backing of former Gov. Michael Dukakis in recent days.

Capuano's other backers includer House Speaker Nancy Pelosi and Reps. Barney Frank, Stephen Lynch, Jim McGovern, Richard Neal, John Olver and John Tierney.

Rep. Niki Tsongas (D-Mass.) is backing the frontrunner in the race, state Attorney General Martha Coakley. The only uncommitted member of the delegation is Rep. Bill Delahunt.

UPDATE: Capuano also got the unexpected backing of the Boston Herald on Tuesday.