US President Barack Obama has made an impassioned plea for a change in gun control laws, at a memorial service honouring the victims of Monday's shooting at the Washington Navy Yard.

Addressing victims' families and officials, he said he had "grieved with five American communities" over mass shootings since becoming president, and warned that there was a "creeping resignation... that this is somehow the new normal".

Twelve people died in the Washington attack, when Aaron Alexis, a former Navy reservist with a history of mental health problems, entered the compound and began shooting.