Eleven parents of children killed in the Sandy Hook massacre will fly to Washington with the president on Air Force One tonight following Obama's speech in Hartford, Conn.

They are coming to Washington to lobby Congress this week to pass measures to combat gun violence.

"There is no more effective advocate than a parent who has lost a child," a senior administration official tells ABC News.

The president, in a speech scheduled to start at 5:45 p.m. tonight in Hartford, will say Congress owes an obligation to these families, and the many other victims of gun violence, to act on his gun control proposals. Obama will meet with the families prior to his speech.

Obama's speech today is just part of the administration's broader effort this week to rally public support for the president's gun-control agenda. The vice president and first lady will participate in gun-control events in the coming days.