Mr Hetherington was best known for his award-winning work in Afghanistan

Two award-winning photographers have been killed while covering the conflict in the Libyan city of Misrata.

Briton Tim Hetherington, 40, is said to have been killed in a rocket-propelled grenade attack.

US photographer Chris Hondros, 41, was also killed, and two others, including Briton Guy Martin, were injured.

Mr Hetherington co-directed the Oscar-nominated war documentary Restrepo. Mr Hondros won the Robert Capa Gold Medal for war photography.

Mr Hetherington co-directed the Oscar-nominated war documentary Restrepo. Mr Hondros won the Robert Capa Gold Medal for war photography.

Mr Hetherington's friend James Brabazon, who worked with him on Restrepo and had been e-mailing him right up until his death, said: "He was extremely talented, experienced and dedicated."

He explained why Mr Hetherington was working for Vanity Fair magazine in Libya: "He went there for humanitarian reasons. He went there to shed light on a very confusing situation."

In a statement on the magazine's website, his family said: "It is with great sadness we learned that our son and brother, photographer and filmmaker, Tim Hetherington was killed in Misrata, Libya, by a rocket-propelled grenade.

His family said he would be "forever missed".

"Tim will be remembered for his amazing images and his Academy Award-nominated documentary Restrepo."

They added: "Tim was in Libya to continue his ongoing multimedia project to highlight humanitarian issues during time of war and conflict."

Vanity Fair magazine said Mr Hetherington was "widely respected by his peers for his bravery and camaraderie" .

In a recent entry on Twitter, Mr Hetherington described "indiscriminate shelling" by pro-Gaddafi forces, who have been battling rebels trying to end the rule of long-time leader Col Muammar Gaddafi.

Mr Brabazon said Mr Hetherington very last Twitter message mentioned that there was "no sign of Nato".

He said: "Although it's an oxymoron to say it, Tim was a very cautious war reporter. He knew the risk but he decided to take them in order to cover the story."

Mr Hondros was based in New York for Getty Images.

The company's director of photography, Pancho Bernasconi, said Mr Hondros had covered conflict zones since the late 1990s including Kosovo, Iraq and Afghanistan.

The White House issued a statement expressing its "deep sadness" at Mr Hondros's death.

"Chris's tragic death underscores the need to protect journalists as they cover conflicts across the globe. Our thoughts are with Chris's family and loved ones," it said.

Cornish photographer Guy Martin, who was working with Panos Pictures agency, was hit by shrapnel and is being treated at a hospital in the city.

The White House said it was deeply saddened about the death of US photographer Chris Hondros

Mr Martin's girlfriend told the BBC his condition had stabilised.

Polly Fields said: "He was in surgery for about six to eight hours. He's come out of that now.

"Now it's a case of getting him stable enough so he can be evacuated from Misrata."

New York-based photographer Michael Christopher Brown was also treated for shrapnel injuries.

A survivor told the BBC that a group of journalists had been pulling back from near the front line during a lull in the fighting in Misrata when they were attacked.

Doctors at a Misrata hospital say they have treated more than 100 casualties, mostly civilians injured by mortar and sniper fire.

Libyan government forces have been battling rebels in Misrata, which is in western Libya, since late February and an estimated 300 civilians have died.

The Foreign Office confirmed Mr Hetherington's death and said it was offering consular assistance to his family.

Mr Hetherington (centre) is assisted by rebels as he climbs down a building hours before his death

Mr Hetherington, who had dual UK and US nationality, studied Literature at Oxford University.

The New York-based journalist was best known for his work in Afghanistan, and the film Restrepo followed US troops on an outpost in the country. He won the World Press Photo of the Year Award in 2007.

Another of Mr Hetherington's friends, Peter Bouckaert from the campaign group Human Rights Watch, said he had a "tremendous reputation and a giant heart".

He told BBC News the journalist had been planning to "slow down" and start a family with his partner.

"I was just with Tim two weeks ago in Benghazi, the rebel capital. At our last lunch together, he told me about the wonderful relationship he was in with this Somali woman and how he wanted to slow down and spend more time making kids," he said.

Vanity Fair editor Graydon Carter said Mr 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 described him as a "rangy, charming workhorse of a photographer".

"Devilishly good-looking and impossibly brave, he was both a ladies' man and a man's man," he said. "There were few like Tim, and there will be fewer like him."

Tributes have started to appear on his Facebook page.

One from film director Jean Manuel said: "Tim Hetherington, I love you. Thank you for everything. I will help make sure our work continues."

The New York-based Committee for the Protection of Journalists (CPJ) said two other journalists had been killed this year in the Libyan conflict.

Cameraman Ali Hassan al-Jaber was shot when his Al-Jazeera crew was ambushed near Benghazi on March 13. Mohammed al-Nabbous, founder of the online Libya Al-Hurra TV, was killed as he was streaming live audio from a battle in Benghazi on March 19.