Tripoli (AFP) - A Dutch journalist was killed by sniper fire Sunday while covering clashes in Libya's coastal city of Sirte, as unity government forces battled Islamic State group holdouts in the jihadist bastion.

Dr Akram Gliwan, spokesman for a hospital in Misrata where pro-government fighters are treated, told AFP that photographer Jeroen Oerlemans was "shot in the chest by an IS sniper while covering battles in Sirte" 450 kilometres (280 miles) east of Tripoli.

Gliwan said his body had been transferred to Misrata, 200 kilometres west of Sirte.

Oerlemans was working in Libya for a number of organisations, including the Belgian weekly Knack magazine, which confirmed his death.

A message on Knack's website said Oerlemans was shot on a reporting assignment and that the publication "wishes his family much strength".

Dutch foreign minister Bert Koenders also mourned his death.

"Oerlemans is a journalist who went where others would not go. He was driven to bring us the news through his pictures especially from the world's trouble spots," Koenders said in a statement.

"That he has now paid the highest price is incredibly sad. I wish his wife, children and family every strength at this great loss. A great photographer is gone."

Forces allied with Libya's UN-backed Government of National Accord launched an assault against the jihadists in Sirte in May.

IS fighters holed up in the town, birthplace of ousted Libyan dictator Moamer Kadhafi, responded with suicide bombings and sniper fire, slowing the government-backed advance.

Fighting on Sunday killed at least 10 IS fighters and eight pro-government fighters around the jihadist bastion, the unity government in Tripoli said.

Pro-government forces said they were "progressing" in Sirte, where they have surrounded IS militants, prompting some to try to escape.

They said loyalist fighters had recovered the bodies of at least 10 jihadists and were chasing another group that had fled Sirte.

- Loyalist casualties -

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Eight soldiers loyal to the GNA were killed, according to the Facebook page of a field hospital set up by their forces in Sirte.

Fifty-seven members of the pro-GNA forces were wounded and transferred to the main hospital in Misrata.

IS said on Twitter that it had killed or wounded 64 members of the pro-GNA forces.

On Saturday, GNA aircraft conducted six sorties in preparation for an advance on the jihadists' hideout in the city's east, said the GNA statement.

American aircraft have also carried out some 177 air strikes since early August in support of GNA forces, according to US Africa Command (AFRICOM).

The fighting has left more than 450 GNA fighters dead and 2,500 wounded. The IS death toll is not known.

An IS defeat in Sirte would be a serious blow to the group, which has faced major setbacks in Iraq and Syria in recent months.

Libya was plunged into chaos following the NATO-backed ouster of Kadhafi in 2011, and the control of the country -- as well as access to its vital oil wealth -- is divided between rival governments and militias.

The GNA was formed following a UN-backed deal in December 2015, but it has struggled to impose its power across a country.

Oerlemans was the second journalist to be killed in the Sirte offensive, after Libyan journalist Abdelqader Fsouk was killed there in July.

British war photographer Tim Hetherington was killed in April 2011 in a mortar attack in the western Libyan city of Misrata.

He died alongside Chris Hondros, a 41-year-old US photographer for Getty, as the pair covered intense fighting between Kadhafi's forces and rebels.