(CNN) -- Oscar nominee Tim Hetherington and acclaimed photojournalist Chris Hondros died Wednesday while chronicling the gritty violence in the war-torn city of Misrata in Libya, their agencies said.
Two other photographers were hurt in the incident, according to news reports.
"The only thing we know is that he (Hetherington) was hit by an RPG with the other guys," said CSPR agency president Cathy Saypol. An RPG is a rocket-propelled grenade.
Hetherington's last Twitter entry appears to have been made on Tuesday: "In besieged Libyan city of Misrata. indiscriminate shelling by Qaddafi forces. No sign of NATO."
See photos of Wednesday fighting in Misrata
A British native who was based in Brooklyn, New York, Hetherington received an Academy Award nomination this year for "Restrepo," a documentary film he co-directed with journalist Sebastian Junger. Employed by Panos Pictures, he also worked in Afghanistan two years ago with CNN's Anderson Cooper and Dr. Sanjay Gupta.
Vanity Fair magazine, where Hetherington, 41, was a contributing photographer, described him as "widely respected by his peers for his bravery and camaraderie." Its profile says he had dual U.S. and British citizenship.
"We are saddened beyond words," Saypol told Vanity Fair.
Read the Vanity Fair article
Hondros suffered a severe brain injury, according to The New York Times, which had a reporter in the hospital and spoke to a colleague at a triage center.
Getty Images, Hondros' employer, said it was "deeply saddened" by his passing:
"Chris never shied away from the front line having covered the world's major conflicts throughout his distinguished career and his work in Libya was no exception. We are working to support his family and his fiancee as they receive this difficult news, and are preparing to bring Chris back to his family and friends in the United States. He will be sorely missed."
Guy Martin, a British citizen working for the Panos photo agency, had shrapnel wounds and was undergoing vascular surgery Wednesday night, according to the same account. Michael Christopher Brown, suffered shrapnel injuries but his life was not in danger, according to the Times.
CNN is working to independently verify the conditions of the wounded.
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Vanity Fair released a statement from Hetherington's family Wednesday.
"It is with great sadness we learned that our son and brother, photographer and filmmaker Tim Hetherington, was killed today in Misrata, Libya, by a rocket-propelled grenade," the statement said. "Tim will be remembered for his amazing images and his Academy Award-nominated documentary 'Restrepo.'
"Tim was in Libya to continue his ongoing multimedia project to highlight humanitarian issues during time of war and conflict. He will be forever missed."
James Hider, Middle East correspondent for the Times of London, told CNN the four journalists were covering fighting on Tripoli Street in Misrata.
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Hider said he was at a hospital and saw Hetherington die in a triage tent. "It was shocking."
The journalists, including Hetherington, had traveled by boat from Benghazi to Misrata on Saturday, enjoying jokes and making sandwiches for refugees, Hider said.
The office of the White House press secretary expressed concern about the safety of journalists in the country. "The Libyan government and all governments across the world must take steps to protect journalists doing this vital work," it said in a statement.
Hetherington spent eight years in West Africa and had reported on social and political issues worldwide, most notably the Liberian conflict.
Watch a slide show from Afghanistan narrated by Hetherington
He gained wide fame for "Restrepo," which chronicles the deployment of a platoon of U.S. soldiers in Afghanistan's Korengal Valley, according to the film's website.
His website says he is interested in "creating diverse forms of visual communication and his work has ranged from multi-screen installations, to fly-poster exhibitions, to handheld device downloads."
"The movie focuses on a remote 15-man outpost, 'Restrepo,' named after a platoon medic who was killed in action. It was considered one of the most dangerous postings in the U.S. military," his website says.
"This is an entirely experiential film: the cameras never leave the valley; there are no interviews with generals or diplomats. The only goal is to make viewers feel as if they have just been through a 90-minute deployment. This is war, full stop."
Biographical material on the "Restrepo" site says Hetherington had reported on conflict and human rights issues for more than 10 years.
"He was the only photographer to live behind rebel lines during the 2003 Liberian civil war -- work that culminated in the film 'Liberia: an Uncivil War' and the book 'Long Story Bit by Bit: Liberia Retold' (Umbrage 2009), and his work for Human Rights Watch to uncover civilian massacres on the Chad / Darfur border in 2006 appeared in the documentary 'The Devil Came on Horseback,'" his biography on the "Restrepo" website says.
In 2006, he took a break from image-making to work as an investigator for the U.N. Security Council's Liberia Sanctions Committee, Human Rights Watch said.
"Restrepo" was his directorial debut and won the Grand Jury Prize at the 2010 Sundance Film Festival. He has won many other awards.
"Diary," his most recent film, is "a highly personal experimental short."
In Memoriam: Tim Hetherington's view of Afghanistan
CNN National Security Analyst Peter Bergen described Hetherington as humble, modest and a gentleman capable of taking gritty photos of combat.
" 'Restrepo' was a labor of love for Tim. He had a great deal of empathy for the young soldiers he documented," Bergen wrote Wednesday. "The resulting film is not only the best documentary about war I have ever seen, it is simply one of the greatest of all war films, sharing the epic quality of movies like 'Apocalypse Now' or 'Full Metal Jacket.' It is also very beautifully shot, revealing Tim's great sense of picture composition."
Born in Liverpool and a student of literature at Oxford University, the photojournalist returned to college to study photojournalism.
Vanity Fair magazine said Hetherington won the World Press Photo Award in 2007 for his coverage of American soldiers in Afghanistan for the magazine.
"We're shocked and saddened by word that our colleague Tim Hetherington has died, and we extend our deepest condolences to his family and colleagues," said Robert Mahoney, deputy director of the Committee to Protect Journalists, a watchdog group. "The Libyan conflict is proving to be an extremely dangerous story for journalists to cover."
Before these casualties were reported, the CPJ had documented more than 80 attacks on the press since political unrest erupted in Libya. Its website has a running list of attacks on media people since February 16. In one well-publicized incident, four New York Times journalists were abducted and freed last month. They described "beatings and abuse while in captivity."
After Hetherington's death, Jalal al Gallal, a spokesman for the rebels, issued a statement saying, "This is no longer the Gadhafi regime taking on Libya's people. This is Gadhafi taking on the world. He has spared no one, not women, not children, not journalists. This is now everybody's war."
The fighting in Misrata -- a northwestern city with an estimated population of 300,000 -- symbolizes the pro- and anti-Gadhafi conflict, and the bloodshed and destruction are worse there than in other Libyan cities.
Many observers believe the besieged city is becoming like Sarajevo, the Bosnian city placed under attack by Serbian forces during the Balkan wars in the 1990s.
In fact, the office of Navi Pillay, the U.N. High Commissioner for Human Rights, said Wednesday that some of the Libyan government's attacks on Misrata could constitute international crimes.
A statement from the office said it condemned "the reported repeated use of cluster munitions and heavy weaponry by Libyan government forces in their attempt to regain control of the besieged city of Misrata, and said that such attacks on densely populated urban areas, resulting in substantial civilian casualties, could amount to international crimes."
CNN's Joe Sterling, Chelsea J. Carter, Katy Byron, Phil Gast and Jennifer Deaton contributed to this report.