For the second time in a less than a week, U.S. warplanes bombed a radar site in southern Iraq Tuesday in another attempt to disable increasingly effective air defenses used against allied pilots, the Pentagon said.

Tuesday's strike was much smaller than an attack by dozens of British and American allied planes against three sites Friday and a strike by 24 allied planes against five targets in February, said Pentagon spokesman Bryan Whitman.

The 8:15 am. EDT strike Tuesday targeted only one site, a fire-control radar that helps Iraq guide its missiles and is located near An Nasiriyah, about 170 miles southeast of Baghdad.

Friday's strike was against Iraqi military communication, radar and missile sites.

Air Force F-16s bombed the site with precision guided munitions and returned safely to their base, Whitman said.

"This radar has been an element of the Iraqi air defense system that has been directly contributing to effectiveness of their integrated air defense system," he said.

In Iraq, the air defense spokesman, quoted by the Iraqi News Agency, confirmed the raid but made no mention of casualties. He said the U.S. and British planes flew out of Saudi Arabia and Kuwait with the support of the governments of those countries.

Iraq in recent months has stepped up efforts to shoot down the allied planes patrolling "no fly" zones in both southern and northern Iraq. The patrols began shortly after the end of the 1991 Gulf War to protect Shiite rebels against attacks by government forces and to keep Iraqi President Saddam Hussein from threatening his neighbors.

"If Iraq were to cease its threatening actions, coalition strikes would cease as well," said a statement from the U.S. Central Command at MacDill Air Force Base, Fla.

There have been more than 1,000 separate incidents of Iraqi surface-to-air missile and anti-aircraft artillery fire against coalition aircraft in the two zones since December 1998, including more than 375 this year, officials have said. Allied planes have struck back two dozen times, with the largest raids being in February and last week.

Officials have said that Iraq has rebuilt its air defenses since U.S. and British warplanes attacked radar and communications targets around Baghdad on Feb. 16 and had been getting better at targeting allied patrol planes.