President Barack Obama secretly authorized the sale of 55 powerful bunker-busting bombs to Israel, Newsweek magazine reported Friday.

Israel first asked to buy deep-penetrating GBU-28 bombs in 2005, but were rebuffed by then-president George W. Bush. At the time the Pentagon had frozen joint US-Israeli defense projects, fearful that Israel was transferring advanced military technology to China, Newsweek said.

However in 2007 Bush informed then-Israeli prime minister Ehud Olmert that the bombs would be ready for delivery in 2009 or 2010, even though the Israelis wanted them immediately.

Obama released the bombs in 2009, the magazine reports, citing unnamed officials familiar with the still-secret decision.

Newsweek, citing unnamed US and Israeli officials, said in its online edition that Israel has developed its own bunker-buster technology, but that it was cheaper to buy the US weapons.

The 2,000-pound bombs are designed to destroy hardened targets, which could be used to strike Iranian nuclear sites.

The Pentagon declined to confirm or deny the report but press secretary George Little said "the United States remains committed to helping Israel provide for its own security and we remain committed to helping Israel maintain its qualitative military edge."