The much-vaunted "Screaming Eagles", who had been absent from the first eight days of the war, entered combat action late Friday with a series of Apache strikes "in the vicinity" of the city, about 80 kilometres (50 miles) southwest of Baghdad, the 101st's Aviation Brigade commander, Colonel Greg Gass, told AFP.

Gass said the airforce also joined the attack, but did not give details on their role.

"We worked closely with the airforce and it was a success," he said.

Gass said the crack Medina Division of Iraq's Republican Guard was known to be near Karbala, but did not say the attack was aimed specifically at its troops or armour, nor did he give details of the targets destroyed.

"We can't say what we hit but, yes, they (Medina forces) are in the area," he said.

Iraq's Medina Division, which played a leading role in the invasion of Kuwait that led to the 1991 Gulf War, is an armoured division, reportedly with more than 200 Russian T-72 tanks.

The Apaches, with their Hellfire missile capabilities, are regarded as the best helicopters for taking out heavy armour, especially tanks.

The night assault followed an attack by F/A-18 Hornet and F-14 Tomcat fighters from the USS Kitty Hawk aircraft carrier earlier in the day on an area between Karbala and Baghdad, officers said.

The warplanes dropped a mixture of 16 1,000-pound (450-kilo) laser-guided bombs, four satellite-guided bombs and three 1,000-pound unguided dumb bombs, on targets that included tanks, helicopters and "a building", Lieutenant Junior Grade Nicole Kratzer said. She gave no further details.

Karbala is regarded as important in the US military's advance towards Baghdad, with the 3rd Infantry Division positioned on the outskirts of the city and apparently poised to take advantage of Friday's air assault.

Officers within the 101st Aviation Brigade said the Apache pilots met some resistance on Friday night, with some aircraft taking hits, but Gass said all pilots returned to their base in southwest Iraq safely.

However two of the 20-million-dollar Apaches crashed at their forward operating base - one on take off and one as it came into land. Officers said the pilots did not sustain serious injuries although the helicopters were severely damaged.

Karbala and Najaf, about 160 kilometres southwest of Baghdad, hold massive importance for Shiites, with sacred shrines that attract thousands of pilgrims each year.

Karbala is where Imam Hussein, the Shiite martyr and grandson of the prophet Muhammad, was killed and buried in 680 AD. Hussein was killed fighting for the right to lead all Muslims and his death was the final act in the schism between Shiite and Sunni Muslims that exists to today.

Najaf, where fighting has raged throughout the week with US officials reporting 1,000 Iraqis killed, is the burial site of Hussein's father and the founder of the Shiite sect, Imam Ali, who was also Muhammad's son-in-law.

Although Shiite Muslims make up 60 percent of Iraq's population, they have been consistently persecuted under the rule of Iraqi President Saddam, who is a Sunni.

Gass said the pilots under his command had been instructed to avoid striking any religious sites.

"We are very well aware of Karbala's historical customs and the religious importance it holds for the Shiites," Gass said before the attack.

"The last thing we want to do is cause any type of damage to Karbala and the Iraqi populace."

WAR.WIRE