US President Barack Obama has announced he is releasing an additional 70 million dollars in military aid for Israel. The stepped-up American aid, first announced in May, will go to help Israel expand production of the Iron Dome rocket defense system, which has proved successful at intercepting rockets fired from the Gaza Strip toward southern Israeli towns and cities. Obama announced the new military assistance on Friday as he signed a bill in the Oval Office expanding military and civilian cooperation with Israel. He said it underscores Washington's "unshakeable commitment" to Israel. Obama noted that Defense Secretary Leon Panetta would visit Israel soon to discuss further cooperation at a time of what he called "heightened tensions in the region." Political commentators in the US noted that the previously announced move by Obama appeared timed to upstage Republican rival Mitt Romney's trip to Israel this weekend. The presumptive Republican nominee is a critic of Obama's policy toward Israel, and has promised to ramp up US aid to Israel. A Romney spokesperson said the former Massachusetts governor was happy to see steps being taken to enhance security cooperation with Israel, adding that "unfortunately, this bill does nothing to address" what she called the White House's evasiveness on whether President Obama recognizes Jerusalem as the capital of Israel. Obama, who won 78 percent of the Jewish vote in the 2008 presidential election visited Israel as a candidate during that campaign, but has not done so as president.