Two international rights groups have called on Libya to release the body of a slain South African photojournalist, whose New Zealand family is still coming to terms with the death.

Anton Hammerl, 41, who lived in London, was shot in the stomach and abandoned in the Libyan desert by forces loyal to Muammar Gaddafi on April 5, family friend Bronwyn Friedlander said in London.

Two American journalists and a Spanish photographer, who were with him at the time, were taken captive.

His family believed Mr Hammerl was detained, but his colleagues confirmed his death after being released in Tripoli on Thursday.

Human Rights Watch and the Committee to Protect Journalists in a joint statement said under international law Libya was obliged to take all feasible measures to account for persons reported as missing as a result of fighting and provide their family members any information it had regarding their fate.

"Libyan government forces killed Anton Hammerl six weeks ago and then lied about what happened," Human Rights Watch emergencies director Peter Bouckaert said.

"They had his passport and they knew he was dead. Now they should at least release his body and provide some truthful answers about his fate."

Mr Hammerl's cousin Jenny Cutting, who lives in Hawke's Bay, told Radio New Zealand today family were struggling with the news.

She said they were considering sending a family member to England to be with his wife and children.

According to the released journalists, Mr Hammerl was left behind bleeding on the outskirts of the eastern oil town of Brega while they were taken by Gaddafi forces.

"His injuries were such that he could not have survived without medical attention," Ms Friedlander said.

The American reporters, James Foley and Clare Gillis, spoke by telephone with Mr Hammerl's wife in London late on Thursday.

Mr Hammerl had three young children and had lived in Britain for five years.