The United States has turned down an Israeli request for "bunker buster" bombs and mid-air refueling planes for fear they could be used to attack Iran, according to the Israeli Haaretz newspaper.

The U.S. administration also refused to give permission for Israeli fighter jets to fly over Iraq -- the quickest route to Iran, it said.

Israel, the region's sole, though technically undeclared nuclear armed state, considers Iran its main strategic threat because of its own alleged atomic program, which Israel and its main U.S. ally suspect is aimed at developing weapons.

The U.S. National Intelligence Estimate, however, found that Iran had stopped its nuclear weapons program in 2003.

Iran has repeatedly denied the allegations, insisting it wants only to provide electricity for its growing population when its fossil fuels run out.

Military experts believe the GBU-28 "bunker busters" Israel had requested could be effective against Iran's underground uranium enrichment facility at Natanz in central Iran.

The GBU-28 is a 2.2-ton, laser-guided, conventional munition equipped with a powerful warhead that can burrow through more than six meters (20 feet) of concrete and up to 30.5 meters (100 feet) of hard ground.

Israeli Defense Minister Ehud Barak said after a meeting with U.S. Secretary of State Condoleezza Rice last month that the United States "do not want, for the time being, any (military) action against Iran" but that Israel kept all options open.

While denying the requests for "bunker-buster" bombs and refueling planes, the U.S. administration has agreed to help reinforce Israel's defenses.

An advanced U.S. radar system is to be stationed in Israel which would double the 2,000-kilometer (1,250-mile) detection range of missiles launched from Iran.