Chaos and carnage broke out at the Palestine Hotel in Baghdad Tuesday as an American tank shell slammed into the offices of Reuters news agency.

Cameramen from Reuters and Spanish television died and three other Reuters staff were wounded in the shelling. A journalist from al-Jazeera was also killed in what the Arab television channel said was a U.S. air strike on its office.

The U.S. military has claimed that enemy fire was coming from both locations when they were attacked. They said they regretted any casualties but retained their inherent right to self-defence.

"When they were fired at, they not only had the right to respond, they had the obligation to respond," Maj.-Gen. Stanley McChrystal told a news briefing.

"We are at war. There is fighting going on in Baghdad. Our forces came under fire. They exercised their inherent right to self-defence," Pentagon spokeswoman Victoria Clarke said.

Reporters at the scene disputed the U.S. military's account.

"I never heard a single shot coming from any of the area around here, certainly not from the hotel," British Sky television's correspondent David Chater told Reuters.

Al Jazeera says it's well known that the Palestine Hotel has served as a base for most journalists covering the war from Baghdad since the bombing began, and suggested the attack may have been deliberate.

"I don't know exactly what can prove that it was not an intentional attack, we are still waiting for more clarification on the American side," said Ibrahim Hilal, chief editor at al Jazeera.

The Committee to Protect Journalists (CPJ) said it believed the U.S. strikes on known media locations violated the Geneva Conventions. The watchdog group outlined its concerns in a letter to U.S. Defense Secretary Donald Rumsfeld.

"While U.S. officials have expressed regret for the loss of life in these attacks and stated that they do not target journalists, they have left the impression that they bear no responsibility for protecting journalists operating independently in Iraq," the letter said.

At his Centcom briefing today in Doha, Qatar, Brig. Gen. Vincent Brooks said that while embedded journalists receive protection from the military, "those who operate as non-embeds do so at their own risk."

A Red Cross spokesman disputed the U.S. claim that the Palestine Hotel was being used as a military base by the Iraqis. "We were never, ever aware of any military activity from there," he said in an interview with BBC.

Since the war began, 10 journalists have been killed in combat situations. News organizations and the CPJ are now calling on U.S. Central Command to investigate the most recent deaths in Baghdad.

"We remind you that journalists are civilians and protected under international humanitarian law and cannot be deliberately targeted," the CPJ letter said.

"While sources in Baghdad have expressed deep skepticism about reports that U.S. forces were fired upon from the Palestine Hotel, even if that were the case, the evidence suggests that the response of U.S. forces was disproportionate and therefore violated international humanitarian law."

With a report from Associated Press