President Barack Obama has signed a bill which will give Israel an additional $225m (£134m) to upgrade its Iron Dome missile defence system.

The bill was passed by Congress with a 395-8 vote in favour on 1 July and is intended to help the country replenish the system which has helped intercept rockets fired at Israel from Gaza by Hamas militants since the conflict began on 17 July.

Officials in Israel claim the Iron Dome – a project the US has already invested hundreds of millions of dollars in – has a success rate of as much as 90%.

Obama signed off the latest deal as Israel and Gaza began a 72-hour ceasefire.

Speaking at a news conference as the bill was approved by Congress, Obama said the funding will go towards Israel's right to defend itself.

"Not only have we been supportive of Israel in its right to defend itself, but in very concrete terms – for example, in support for the Iron Dome program that has intercepted rockets that are firing down on Israeli cities – we've been trying to cooperate as much as we can to make sure that Israel is able to protect its citizens," he said.

White House spokesperson Josh Earnest added: "The United States is proud that the Iron Dome system developed in coordination with Israel and funded by the United States has saved countless Israeli lives.

"Continued bipartisan support for Iron Dome funding ensures Israel will retain vital defence against rockets and artillery in light of the enduring threats."

The American Jewish Committee expressed its "heartfelt appreciation" to the US for approving additional funding to Israel's defence system.

"Iron Dome has been a genuine life-saver for Israelis enduring round-the-clock barrages of Hamas rockets and missiles from Gaza," said AJC executive director David Harris. "Thankfully, Congress, in the spirit of its long support for the US-Israel relationship, recognizes the essence of the ruthless Hamas threat to Israelis of all ages."

The deal was signed following confirmation the US resupplied Israel with weapons and ammunition 12 days after the conflict began.

Israel made a request to withdraw 120mm mortar rounds and 40mm ammunition for grenade launchers from a US stockpile inside the country known as the War Reserves Stock Allies-Israel (WRSA-I).

The stock inside WRSA-I usually can only be withdrawn in an emergency. However, an anonymous source told Reuters the shipment of ammunition to Israel was allowed as it was an opportunity for the US to replenish its stock.

"They didn't ask for it from there [WRSA-I] but we gave it to them so we could rotate our stocks," the source said.