WASHINGTON -- At least one B-1 bomber struck Iraqi radars in western Iraq Friday, the first time a long-range bomber has been used in a combat mission to enforce the no-fly zones over Iraq, U.S. defense officials said.

The use of a heavy bomber for a routine mission normally conducted by fighter jets was another sign that U.S. forces are stepping up the pressure on Baghdad as President George W. Bush heads into a weekend summit in the Azores to discuss Iraq with his British and Spanish counterparts.

The B-1s targets were "a couple of radars out west," said a defense official, speaking on condition of anonymity.

It was not immediately clear if one or two B-1 bombers were used in the raid.

"They've never been flown before in Operation Southern Watch," another defense official said, referring to the 12-year-old mission to enforce a no-fly zone south of the 33rd parallel.

With between 600 and 700 U.S. combat aircraft now massed around Iraq, U.S. air forces are flying hundreds of missions a day in the south to get used to the terrain and to keep Iraqi forces off balance as to the timing of a U.S. air assault.

B-2 Stealth bombers, which deployed Thursday from their home base in Missouri to positions closer to Iraq, are the latest addition to the U.S. strike force.

The B-1 bomber, which was designed to penetrate air defenses of the now-defunct Soviet Union by flying below radar at supersonic speeds, can carry up to 24 satellite-guided 2,000 pound bombs.

It made its combat debut in Iraq in 1998 during a four-day bombing campaign precipitated by an earlier standoff with Baghdad over UN inspections. It flew in the NATO air war against Yugoslavia in 1999 and in last year's conflict in Afghanistan. (AFP)