US President Barack Obama made a show of support for Israel at the White House on Friday, ahead of a weekend visit to the US ally by Republican presidential rival Mitt Romney.

Surrounded in the Oval Office by representatives of the pro-Israel lobby AIPAC and by US lawmakers, Obama signed a law reinforcing US security and military cooperation with Israel.

Israeli journalists were invited to attend the signing along with photographers and reporters accredited to the White House. Such signing ceremonies have been uncommon in the Obama presidency.

The law, which gives Israel preferential access to US arms and munitions, "underscores our unshakable commitment to Israel's security," Obama said.

The president also saluted a $70 million US contribution this year to Israel's Iron Dome missile defense system, designed to protect the country against rocket attacks from Islamist militants in Lebanon and Gaza.

The program has received $205 million in US funding since its inception.

Obama said it had been "critical in terms of providing security and safety for Israeli families, it is a program that has been tested and has prevented missile strikes inside of Israel."

"I hope that as I sign this bill, everybody understands how committed all of us are -- Republicans and Democrats, as Americans -- to our friends to make sure that they're safe and secure."

The ceremony came on the eve of a visit to Israel by Romney, who is expected to arrive there over the weekend, the second stop on an international trip aimed at burnishing his foreign policy credentials.