WASHINGTON - President Barack Obama has signed a bill granting an additional $225 million in U.S. taxpayer dollars for Israel's Iron Dome missile defence system.

The defence system has been highly effective in the current round of violence between Israel and Hamas militants in the Gaza Strip. It allows Israel's military to shoot down incoming rockets or mortars headed toward major population centres in Israel. Israeli officials say it has a success rate as high as 90 per cent.

The U.S. has provided hundreds of millions of dollars for Iron Dome in the past. The new package is intended to replenish Israel's capabilities.

Congress approved the money last week before lawmakers left for their annual summer break. Obama signed the bill late Monday in the Oval Office with a handful of photographers present.