"There are inescapable obligations on the parties to the conflict. Human rights and international humanitarian law cannot be put on hold," he said in a statement, repeating an appeal for civilians in Iraq to be protected.

The UN High Commissioner for Human Rights said concern for the welfare of civilians had become "even more relevant as fighting has now engulfed the largest and most densely populated area, the capital Baghdad".

"This conflict has once again reminded us of the cruelty of war and that the innocent are invariably its main victims," Vieira de Mello said.

Aid agencies have warned that hospitals in the Iraqi capital are being overwhelmed by the sharp growth in casualties since fighting reached the streets of Baghdad.

On Tuesday, a journalist from Arab television station Al-Jazeera, as well as two cameramen from the Reuters news agency and a Spanish television station, Telecinco, were killed in incidents involving US forces.

Three other journalists were wounded. Twelve media staff have been killed while covering the conflict that began March 20.

"The right to freedom of information is dealt a fatal blow whenever a journalist is killed or wounded in the performance of his or her vital role," Vieira de Mello said.

SPACE.WIRE