According to the evening daily Kayhan, an American fighter entered Iranian air space Thursday night, flying over the southern border strip at Iran's Mousa-Abad region for several minutes.

The US warplane flew back to Afghanistan, from where it had entered the Iranian airspace, the paper added.

Kayhan further quoted an unknown source as saying that three US warplanes had again violated Iranian air space in the southwestern cities of Khorramshahr and Abadan near the Iraqi border.

"The three warplanes, of F-18 Hornets and F-16 Tomcats types, held overflights at high altitudes near the Khorramshahr and Abadan air borders.

"The circular maneuvering of the two American fighters indicated them as carrying out spying sorties and controlling the borders," the paper quoted the source as saying.

The report came less than a week after Iran's Air Force chief, Brigadier Karim Qavami was quoted as having ordered the forces under his command to open fire and shoot down any unidentified aircraft violating the country's air space.

"Given that the intrusion of enemy aircraft over Iran's air space is possible, all fighter jets of the country have been ordered by the Army chief to shoot them down in the event of sighting them," the daily Kayhan quoted Qavami as saying last Saturday.

The Air Force chief stressed that 'any flight (within Iranian air space) must be coordinated, or else it will be targeted', the daily added.

Iran has been wary of the occupation forces' presence on its doorsteps in Iraq and have had their movements under close scrutiny.

In August, press reports said that five US warplanes had entered Iran's air space from the southwestern Shalamcheh border and flown over the city of Khorramshahr.

According the Persian daily Seday-e Edalat, 'the jet fighters which flew at high speed and altitude, then headed to the Arvand River'.

"While the objective of the fighters' violation of Iranian air space is not known yet, some military specialists believe such moves are aimed at assessing the sensitivity of the Islamic Republic's anti-aircraft defense system," the paper said at the time.

In June, Iranian naval guards seized three British boats with eight crew in the country's territorial waters in Arvand river, which borders Iraq.

The servicemen, two Royal Navy sailors and six Royal Marine commandos, were later released.

Qavami also reiterated the readiness of the Iranian air force to confront any foreign threat to the country's nuclear sites.

"We have made planning not only for nuclear centers but also for sensitive and strategic sites," Kayhan quoted him as saying.

His statements came days after army chief General Mohammad Salimi was quoted as saying that the air force has been ordered to be prepared to defend the country's nuclear sites in the event of an attack.

"The air force has been ordered to protect the nuclear sites, using all its power," the daily Iran quoted Salimi as saying, adding the air force had temporarily suspended all its maneuvers in order to focus its capabilities on patrolling the skies over Iran.

Such statements have raised the stakes in a war of words amid foreign press speculation about possible Israeli and American attack on Iran's nuclear facilities.

Iranian military commanders have warned of grave consequences if any such attack takes place.

Israeli Defense Minister Shaoul Mofaz was cited to have tried to 'calm things down' concerning the possibility of the Zionist regime striking Iranian nuclear installations.

"We have to calm things down concerning the so-called intentions attributed to Israel of attacking Iran," AFP quoted Mofaz as saying.