Two leading photojournalists have been killed covering escalating violence in Misrata, and two other western photographers working with them were injured.
Oscar-nominated British documentary-maker Tim Hetherington, 40, co-creator of the Sundance-winning documentary Restrepo, was killed covering fighting between Muammar Gaddafi's forces and the opposition.
Chris Hondros, 41, a US Pulitzer nominee who works for Getty Images, was also killed. His work has appeared in magazines and newspapers around the world. His awards include World Press Photo honours and the Robert Capa Gold Medal, one of the highest prizes in war photography.
The British photographer Guy Martin, who works for the Panos agency, was critically injured. The fourth man was reported by the New York Times to be photographer Michael Christopher Brown, but his condition was not said to be life-threatening.
According to colleagues at the scene, Hetherington and Hondros were among eight to 10 journalists reporting from Tripoli Street in Misrata yesterday afternoon. When shooting broke out, they took shelter against a wall, which was hit by fire. Hetherington died soon after arriving at hospital.
Hetherington wrote in his last post on Twitter on Tuesday: "In besieged Libyan city of Misrata. Indiscriminate shelling by Gaddafi forces. No sign of Nato."
His family issued a statement: "It is with great sadness we learned that our son and brother, photographer and film-maker Tim Hetherington, was killed today in Misrata, Libya by a rocket-propelled grenade.
"Tim will be remembered for his amazing images and his Academy award-nominated documentary Restrepo. Tim was in Libya to continue his multimedia project to highlight humanitarian issues during time of war and conflict. He will be for ever missed."
The journalist and film-maker James Brabazon, a close friend of Hetherington, told BBC2's Newsnight: "Tim was a leading light of his generation – it's really not an exaggeration to say that his eye and his ability, what he did, was unique.
"His reportage really defined a generation of covering conflict.
"The main thing about Tim to understand is that he was fundamentally a humanitarian. A lot of the work that he did wasn't just for the news or for magazines, but was for human rights organisations as well."
"Right now I think what Tim would be concentrating on, as much as anything, is the plight of the civilians in Misrata. That's why he was there, to tell their story."
Vanity Fair editor Graydon Carter said Hetherington was "about as perfect a model of a war photographer as you're going to find these days".
In an editorial for the magazine he said: "He was a rangy, charming workhorse of a photographer."
"There were few like Tim, and there will be fewer like him. He had a deft eye and unwavering dedication."
Peter Bouckaert, a friend of Hetherington's who works for Human Rights Watch in Geneva, said Hetherington had been planning to "slow down" and start a family with his partner. "He really was a person who cared very deeply for the civilians affected by conflict," he told BBC News.
Tyler Hicks, a photographer for the New York Times who worked alongside Hondros, said: "Chris made sacrifices in his own life to bring the hardships of war into the public eye, and that dedication created award-winning photographs that shaped the way people viewed the world. I'm grateful to be among the many people who were lucky enough to know him. He will be missed."
"I was just with Tim two weeks ago in Benghazi, the rebel capital. I had my last lunch with him and he told me about the wonderful relationship he was in with this Somali woman and how he wanted to spend more time and slow down and make kids. It is a tremendous loss."
Andre Liohn, a colleague of the photographers who said he was at the hospital in Misrata where they were taken, wrote on his Facebook page yesterday afternoon: "Sad news Tim Hetherington died in Misrata now when covering the front line."
Liohn added an hour later: "Chris Hondros died now."
Hetherington and Hondros are believed to be the first western journalists killed covering the conflict. The al-Jazeera cameraman Ali Hassan al-Jaber was killed when fighters ambushed his car as he travelled to Benghazi on 12 March. Mohammad Nabbous, a reporter for Libya Alhurra TV, was killed seven days later in Benghazi.
The Committee to Protect Journalists said about 10 journalists have been killed covering the Arab Spring uprisings this year out of 14 deaths worldwide.
The international criminal court warned Libyan authorities about the treatment of journalists yesterday. Around 16 journalists are missing in the country, it said.
Liverpool-born Hetherington won numerous awards for his coverage of conflict zones. Restrepo, a war documentary following a platoon of US troops in Afghanistan, won a prize at the Sundance film festival this year. Hetherington co-directed it with journalist Sebastian Junger.