Two photographers, including one who was nominated for an Academy Award for a documentary on U.S. soldiers in Afghanistan, were killed Wednesday during heavy shelling in the Libyan city of Misrata.

Tim Hetherington, a Briton who held both U.S. and British citizenship who co-directed "Restrepo," was killed as he covered the fighting between forces loyal to embattled leader Moammar Gadhafi and rebels seeking his ouster.

Later Wednesday, it was reported that Getty Images photographer Chris Hondros, 41, died in hospital hours after sustaining serious brain trauma. Two other photographers -- Guy Martin of the Panos photo agency and Michael Christopher Brown -- were treated in hospital for shrapnel wounds.

The BBC reported that the journalists got caught in a mortar attack near the front line of fighting.

Hetherington was a contributing photographer to Vanity Fair magazine, which posted an obituary to its website Wednesday confirming his death.

Hetherington's U.S. publicist, Johanna Ramos Boyer, confirmed that he had died in Misrata, a rebel-held city in western Libya that has come under heavy attack by pro-Gadhafi forces.

On Tuesday, Hetherington tweeted from Misrata about "indiscriminate shelling" by forces loyal to Gadhafi. "No sign of NATO," he tweeted.

On Wednesday, the news of Hetherington's death followed UN reports that pro-Gadhafi forces were using cluster bombs on rebels in Misrata.

"Reportedly one cluster bomb exploded just a few hundred metres from Misrata hospital, and other reports suggest at least two medical clinics have been hit by mortars or sniper fire," UN High Commissioner for Human Rights Navi Pillay said in a statement.

According to Pillay, targeting medical facilities constitutes a war crime, while targeting civilians is a violation of international law.

Forces loyal to Gadhafi have ramped up their campaign against rebels in Misrata, hammering Libya's third-largest city with tank shells and rockets, sending some into residential areas. Hundreds of people have reportedly been killed in the city over the last weeks of heavy fighting.

Officials with the Gadhafi regime have denied claims the army is using missiles or cluster bombs in the city.

"We welcome any objective investigation of the actions of our army, our government and our officials," said government spokesperson Moussa Ibrahim.

Hetherington, 40, had shot extensively for the magazine in Afghanistan, winning the World Press Photo of the Year Award in 2007 for a photograph taken while covering U.S. soldiers in the Korengal Valley.

Hetherington's time in Afghanistan led to the 2010 documentary "Restrepo," which he co-directed with Vanity Fair contributor Sebastian Junger. The film was nominated in the best documentary category at this year's Academy Awards.

"Hetherington was widely respected by his peers for his bravery and camaraderie," read the In Memoriam posted to Vanity Fair's website, written by David Friend. "His imaginative, even artistic, approach to photojournalistic subjects led to many honors, including a fellowship from the National Endowment for Science, Technology, and the Arts as well as grant from the Hasselbald Foundation."