BAGHDAD, Iraq (CNN) -- More military action took place Saturday over the skies of Iraq as U.S. warplanes attacked six Iraqi military installations inside the northern no-fly zone.

U.S. F-E15 Strike Eagle aircraft retaliated against Iraqi missile sites Saturday afternoon after being targeted during routine flights near Mosul, sources told CNN.

U.S. aircraft responded by dropping what was described as "very heavy ordnances," including GB U-2 precision-guided missiles.

In addition, a U.S. Marine Corps EA-6B prowler fired a high speed anti-radiation speed missile -- a HARM missile -- at Iraqi anti-artillery systems.

Earlier Saturday, an Iraqi air defense unit targeted another F-15E Strike Eagle. The F-15 responded by launching an AGM- 130 missile against the site. Two other F-15Es dropped laser-guided bombs at the same site.

All six attacks -- targeting a radar site and its missile launchers, four anti-aircraft missile sites and a surface-to-air missile site -- took place between 3 p.m. and 4:30 p.m. (1200-1330 GMT).

The Iraqi government released a statement protesting the attacks, and criticized neighboring Saudi Arabia, Turkey and Kuwait for providing bases for coalition forces.

A spokesman for the U.S. base at Incirlik, Turkey, said all planes returned safely to the base. There was no word on possible damage to Iraqi forces .

American and British warplanes have enforced the no-fly zone north of the 36th parallel since the end of the Persian Gulf War in 1991 to protect the Kurdish population there from attacks by Iraqi government forces.

Confrontations between coalition and Iraqi forces in both the northern and southern no-fly zones have been frequent in recent weeks.

Reuters contributed to this report.