UPDATE 1-Nigerian security forces arrest U.S. filmmaker

(Adds military comment)

PORT HARCOURT, Nigeria, Sept 2 (Reuters) - Authorities in Nigeria have charged a U.S. journalist working on a documentary in the oil-producing Niger Delta with spying after he was arrested for filming the army, a media watchdog said on Tuesday.

Andrew Berends, a freelance journalist, was arrested on Sunday for filming a deployment by a joint military taskforce which patrols the region, military spokesman Lieutenant Colonel Sagir Musa said.

"He was handed over to the State Security Services for professional investigation, to simply ascertain his mission and why he intruded into an operational area, snapped video shots of troops and their deployment without clearance," Musa said.

He did not confirm any charge against Berends.

Paris-based Reporters Without Borders said Berends was charged with spying after being arrested in Nigeria's oil hub of Port Harcourt, detained for 36 hours and forced to hand over his passport.

"Berends was arrested for doing his job and no other reason," the rights group said. "This is the third time in a year that baseless charges of spying have been brought against foreign journalists."

Berends, who arrived in Nigeria in April, was released late on Monday with orders to report back to the State Security Services in Port Harcourt on Tuesday. His Nigerian translator, Samuel George, remains in custody.

Armed rebels demanding greater local control over oil revenues launched a wave of attacks in early 2006 in the Niger Delta, where the OPEC member's oil industry is based. The unrest has cut oil production by about a fifth.

In April, security forces arrested four U.S. filmmakers and a Nigerian who were working on a documentary about the oil industry in the delta. They were detained for six days on spying charges before being released to the U.S. embassy. Nigeria's record on press freedom is much better than that of many African countries and journalists freely criticise the government. However, there are occasional incidents of journalists being detained and the SSS has been named a "predator of press freedom" by Reporters Without Borders. (For full Reuters Africa coverage and to have your say on the top issues, visit: africa.reuters.com/ ) (Reporting by Austin Ekeinde; Writing by Randy Fabi; Editing by Nick Tattersall)