* Security forces rescue 13 hostages, including 9 foreigners
* Destroy important militant camp in delta
(Adds comments from rescued hostages, previous Port Harcourt)
By Segun Owen
WARRI, Nigeria, May 16 (Reuters) - Nigerian security forces said on Saturday they rescued 13 hostages kidnapped this week, including nine foreigners, and destroyed a key militant camp in the heart of Africa's biggest oil industry region.
Nigeria's main militant group has declared an "all-out war" and warned oil companies to evacuate their staff in the Niger Delta following three days of heavy clashes with the military.
The army said its forces, using navy gunboats and helicopters, would continue an offensive to flush militants out of the creeks after the hijacking of two oil vessels and attacks on troops in southern Delta state.
Global crude oil markets CLc1 have largely ignored the clashes in the OPEC member country, closing lower in two of the last three sessions.
"We will carry on with our operations until we stabilize the situation," said Colonel Rabe Abubakar, spokesman for the military taskforce in the Niger Delta, adding two soldiers were wounded in this week's fighting.
Royal Dutch Shell (RDSa.L), U.S. oil major Chevron (CVX.N) and other energy companies working in the area were given until Saturday by the militants to remove their workers.
Security sources have said they are taking the militant threats seriously but there are no plans to evacuate more staff.
The military on Friday freed nine Filipinos and four Nigerians that were kidnapped two days earlier when their oil vessel MV Spirit was hijacked by militants near Warri in Delta state, Abubakar said.
A total of 20 people were believed to have been on board the ship chartered by state oil firm NNPC.
The rescued crew members told reporters on Saturday two Filipinos were killed and at least five others wounded by crossfire.
"We thought we were going to die as bombs were coming down from the helicopters, but the rescuers told us not to run," Mathillo Ete, a Filipino crew member wounded in the clashes, told Reuters.
The heavy fighting has centred around a camp belonging to militant leader Government Tompolo who had been involved in negotiations over a possible amnesty with the authorities.
Abubakar said the camp, located along Chanomi Creek in Delta state near Chevron's Escravos export terminal and Nigeria's 125,000 barrels per day Warri refinery, was largely destroyed on Friday in the heaviest fighting in the area in eight months.
"I'm glad to inform you that our search-and-rescue operation conducted in the Chanomi Creek yesterday led to the total destruction of the notorious Camp 5," he said.
Attacks by MEND have cut Nigeria's oil output by about a fifth since early 2006, forced foreign firms to remove all but essential staff and eaten into the country's foreign earnings, exacerbating the impact of the global downturn.
But security experts say the group is smarting from a more muscular military stance in the Niger Delta, while oil bunkering -- the theft of industrial quantities of crude oil and a major income stream for militant groups and criminal gangs -- has become less profitable with lower global energy prices. (For full Reuters Africa coverage and to have your say on the top issues, visit: africa.reuters.com/) (Additional reporting by Austin Ekeinde in Port Harcourt; Writing by Randy Fabi; Editing by Matthew Jones)