In a direct message to Iraqi troops, allied forces on Thursday dropped thousands of leaflets over the southern no-fly zone in Iraq warning gunners to stop firing on U.S. and British patrol planes.

Iraqi forces responded by firing on aircraft delivering the leaflets. That led allied forces to bomb an air defense operations center, U.S. Central Command officials said.

The leaflet drop was the first known direct warning from the Pentagon to Iraq's military rank and file in the Bush administration's campaign to topple Iraqi President Saddam Hussein.

Defense officials said it was not directly related to another leaflet effort in which the Pentagon plans to warn Iraqi officers against firing chemical or biological weapons in the event of U.S. military action to remove Saddam.

The allied retaliation brought to 46 the number of "strike days" reported this year by the coalition force that patrols zones set up to protect Iraqi minorities following the 1991 Gulf War. On some days, more than one area is bombed.

Defense officials said coalition aircraft dropped 120,000 leaflets depicting a jet bombing a missile launcher and a radar site with the message: "Iraqi ADA [air defense artillery] Beware! Don't track or fire on coalition aircraft!"

The back side of the leaflet had another message. "The destruction experienced by your colleagues in other air defense locations is a response to your continuing aggression toward planes of the coalition forces," leaflets written in Arabic said.

"No tracking or firing on these aircraft will be tolerated. You could be next," said an English translation released by defense officials.

"We were telling them 'Don't shoot at us or we'll shoot back,"' said Navy Commander Frank Merriman, a spokesman for Central Command in Tampa, Fla. "And they were shooting at that aircraft that was dropping the leaflets."

He said a similar leaflet drop was done in October 2001 to try to halt the firing on patrol planes. That effort was not publicly disclosed until Thursday.

Another defense official said Thursday's action was not related to any possible war with Iraq, portraying it as done periodically to remind Iraqi gunners that they target coalition planes at their peril.

Central Command said the strike came after Iraq air defenses fired anti-aircraft artillery and surface-to-air missiles at coalition aircraft.

The planes used precision-guided weapons against the operations center and air defense headquarters for the sector near Tallil, about 160 miles southeast of Baghdad, according to a Central Command statement. There was no immediate damage assessment.

Iraq considers the patrols a violation of its sovereignty and frequently shoots at the planes. In response, coalition pilots try to bomb Iraqi air defense systems.

Coalition strikes are not necessarily aimed at the place or equipment used to target them, though officials said Thursday's was. Defense Secretary Donald H. Rumsfeld disclosed recently that he has ordered that pilots attack command and communications links in Iraq's air defense network rather than the guns and radars used to target or shoot at pilots.

The goal of the new approach, more than a decade after enforcement of the no-fly zones began, is to reduce dangers to the pilots while increasing the damage to an air defense system that has grown more sophisticated.

The strike was in the southern zone, set up to protect Shiite Muslims. The northern zone was set up to protect the Kurdish population. Both groups were given protection after unsuccessfully revolting against Saddam.