A media advocacy group says Nigerian authorities have released a U.S. documentary filmmaker and his interpreter who were arrested earlier this week on spying charges.

The New York-Based Committee to Protect Journalists (CPJ) says freelance journalist and filmmaker Andrew Berends and his Nigerian interpreter Samuel George were released into the custody of the U.S. Embassy in Nigeria on Friday.   

Colleagues of Berends confirmed his release. CPJ says the two are expected to report back to authorities on Monday.

Berends and George were arrested August 31 while filming in Port Harcourt, the main city in the Niger Delta region. 

CPJ says Berends was released after 36 hours but was ordered to report back to the State Security Services for interrogations everyday. The group says George remained in custody the entire week.

The CPJ says arresting journalists for doing their jobs is unbefitting of Nigeria's leaders.

The group says New York's two U.S. Senators, Hillary Clinton and Charles Schumer, each wrote to U.S. Secretary of State Condoleezza Rice on the filmmaker's behalf.

Media advocacy groups says this is the third time in a year Nigerian authorities have accused foreign journalists of spying.

Four U.S. documentary filmmakers were arrested and held for four days on spying charges in April.  In September 2007, two German journalists and a U.S. activist were held for two weeks on similar charges.

Militants launched a wave of attacks and kidnappings in the Niger Delta in early 2006.  The groups are demanding that more of the region's oil revenue be directed to impoverished local communities.

The unrest has cut Nigeria's oil production by about 25 percent, contributing to the rise in world oil prices. 

Some information for this report was provided by Reuters.