WASHINGTON -- U.S. and British warplanes attacked Iraqi air defense installations, including a fiber-optic communications node, in southern Iraq Friday in the biggest air strike since a raid last February around Baghdad, Pentagon officials said.

About 50 aircraft, including nearly 20 strike aircraft, launched the attack from the aircraft carrier USS enterprise and air bases in the Persian Gulf in response to recent attacks on coalition aircraft patrolling a no-fly zone over southern Iraq, AFP quoted the officials as saying.

All coalition aircraft returned safely to their bases, they said.

A fiber-optic communications node, a surface-to-air missile site, and a long-range early warning radar were targeted in the raid, said Bryan Whitman, a Pentagon spokesman.

It was not immediately known whether the sites were linked together by fiber-optic cable. But Whitman, said, "All three targets contributed to the effectiveness of Iraq's integrated air defense system."

"We took this action in response to increased provocations in the no-fly zones," he said.

"We've continued to see increased efforts by iraq to shoot down coalition aircraft," he said. "Iraqi forces continue to fire on coalition aircraft on a regular basis. As we've always said, we will strike at the time, and at the place and in the manner of our choosing."

It was the biggest coalition air attack since a February 16 raid that struck command posts and early warning radars around Baghdad in an effort disrupt a fiber-optic linked network being built with the help of the Chinese.

U.S. Defense Secretary Donald Rumsfeld acknowledged last week that Iraq has "quantitatively and qualitatively improved" its air defenses since then, re-installing the fiber optic links to improve the accuracy of its ground fire on U.S. and British aircraft in the south.

The fiber-optic links enable high-volume, high speed transmission of data from early warning radars to the command posts that fire surface-to-air missiles at coalition aircraft.

Army General Tommy Franks, the commander of the U.S. Central Command, initiated Friday's raid and notified his chain of command, said a Pentagon official, who spoke on condition of anonymity.

Franks has the authority to carry out raids in the no-fly zones that he deems necessary to protect his pilots. Some strikes, including those around Baghdad, require White House approval.