WASHINGTON – President Barack Obama said Friday he is releasing an additional $70 million in military aid for Israel, a previously announced move that appeared timed to upstage Republican rival Mitt Romney's trip to Israel this weekend.

The stepped-up U.S. aid, first announced in May, will go to help Israel expand production of a short-range rocket defense system. The system, known as Iron Dome, has proved successful at stopping rocket attacks fired at Israeli civilians from close range, including from Gaza.

Obama announced the new military assistance as he signed a bill in the Oval Office expanding military and civilian cooperation with Israel.