SPECIAL CORRESPONDENT NEW YORK - US President Barack Obama secretly authorized the sale of 55 powerful bunker-buster bombs to Israel, a report by Newsweek magazine says. Experts say the bombs are designed to destroy hardened targets, and could be used to strike Iranian nuclear sites. Newsweek said the bunker-busters are small-sized GBU-39 bombs which have been designed to enable jet fighters to carry more bombs in place of a single one-ton bomb. When Israel first asked to buy deep-penetrating GBU-28 bombs in 2005, the then president George W. Bush refused to sell these bombs because at that time the Pentagon had frozen joint US-Israeli defence projects due to fears of Israel transferring advanced military technology to China, the magazine wrote. In 2007, Bush informed the then-Israeli Prime Minister Ehud Olmert that the bombs would be ready for delivery in 2009 or 2010 despite the fact that the Israelis wanted them immediately. According to the magazine, unnamed officials said that in 2009 Obama authorized the delivery of the bombs. Quoting anonymous US and Israeli officials, Newsweek claimed that Israel has developed bunker-buster technology but considers it cheaper to buy the bombs from the US. The 2,000-pound bombs are designed to destroy hard targets. They are capable of penetrating 6 feet (at least 1.8 meters) of reinforced concrete and more than 3 feet (approximately 1 meter) of steel-reinforced concrete. 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".