President Barack Obama speaks in the Oval Office of the White House in Washington, Friday, July 27, 2012, before signing the United States-Israel Enhanced Security Cooperation Act. From left are, Richard Stone, chairman, Conference of Presidents of Major American Jewish Organizations, Rep. Barbara Boxer, D-Calif., Howard Friedman, past chair of the Board, AIPAC, the president, Rep. Howard Berman, D-Calif., and Lee Rosenberg, chairman of the Board, AIPAC. (AP Photo/Susan Walsh)

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.

As he sought to underscore his commitment to Israel, the president first said the increased aid totaled $70 million, then said the number was actually $70 billion, even though the smaller figure is correct.

Obama said the bill underscores the United States’ “unshakable commitment to Israel.”

The White House focus on Israel this week comes as Romney prepares to visit Jerusalem. The presumptive GOP nominee is a critic of Obama’s policy toward Israel and has promised to ramp up U.S. aid to the Jewish state, although Obama officials say the administration already provides record levels of funding.

A Romney spokeswoman said the former Massachusetts governor was happy to see steps being taken to enhance security cooperation with Israel.

“Unfortunately this bill does nothing to address yesterday’s evasiveness from the White House on whether President Obama recognizes Jerusalem as the capital of Israel, which raised doubt about the president’s commitment to our closest ally in the region,” said Romney spokeswoman Amanda Henneberg.

Romney is in London on the first leg of an overseas trip designed to burnish his foreign policy credentials.

The White House subtly injected itself into Romney’s trip on Thursday after Romney caused a stir by calling London’s problems with Olympics preparation “disconcerting.”

White House spokesman Jay Carney said Obama “has the utmost confidence” in Britain’s ability to host the games.

Obama planned to continue competing with Romney for attention during the opening ceremonies of the Olympic Games, which Romney was scheduled to attend while in London. Romney led the organizing committee for the 2002 Olympics in Salt Lake City.

The Obama campaign was airing an ad for American audiences during the opening ceremonies featuring Obama promoting his middle-class political pitch.

“I believe that the way you grow the economy is from the middle out,” Obama says in the ad, echoing a standard campaign refrain. “I believe in fighting for the middle class because if they are prospering, all of us will prosper.”

With the ad, Obama guarantees himself a presence during opening ceremonies despite the free media Romney might get by being there in person.