ISTANBUL (AFP) - - Three unidentified gunmen and three Turkish policeman were killed in a shootout outside the US consulate in Istanbul, provincial Governor Muammer Guler said Wednesday.

The assailants were killed at the scene, the governor told reporters, adding that they had "directly" targetted the police post outside the high-walled US consulate in the district of Istinye.

One policeman died on the spot, while two others succumbed to their injuries in hospital. Another policeman and the civilian driver of a police truck were injured.

Prosecutors specialising in terrorism cases had launched an investigation into the incident, Guler said, adding that guns and rifles were seized at the scene.

Television footage showed a bloodied body, covered with newspaper, lying in the street.

No consulate personnel were injured, the spokeswoman of the US embassy in Ankara, Kathy Schallow, told AFP.

The three assailants jumped from a white car and opened fire at the police checkpoint around 11:00am (0800 GMT), a witness told NTV television.

The security forces returned fire, killing all three gunmen.

The shootout lasted about eight minutes, witnesses said.

The white car, driven by a fourth accomplice, drove off after the attack and immediately became the target of a major police hunt.

The police post was situated outside a gate for visa applicants from where steep steps lead up to the fortified consulate building.

The consulate was moved to its current high-security location in 2003 as foreign missions across the world enhanced security measures following the September 11, 2001 attacks in New York.

The most recent attack on a foreign mission in Turkey was in 2003 when Al-Qaeda militants detonated a car bomb outside the British consulate in Istanbul, and simultaneously attacked the British HSBC bank.