By Christopher Thompson

LONDON, Feb 21 (Reuters) - A British human rights worker arrested in Angola on a charge of espionage likely will be released from jail on Wednesday but prohibited from leaving the southwestern African nation, an Angolan official said.

Sarah Wykes, an anti-corruption campaigner with Global Witness who was in Angola to investigate transparency in the country's oil sector, has been detained in Cabinda since her arrest early Sunday morning.

"She is still in jail at the moment, but if she pays bail then she can leave today," Luis Camanda, the director of public prosecutions in the oil-rich Angolan enclave, told Reuters by telephone.

Bail has been set at 180,000 Angolan Kwanzas ($2,200), according to one of her lawyers. Wykes was scheduled to appear on Wednesday with her defense team in a court in the provincial capital Cabinda.

If bail is granted, it will likely be accompanied by a travel ban and other restrictions. Camanda said the activist, among other things, would not be allowed to leave Angola without the permission of the government.

Wykes, who arrived in Angola on Feb. 11 and then travelled to Cabinda later the same week, is accused of violating the country's national security, according to the state-run ANGOP news agency.

The charge could cover anything from meeting banned groups to taking pictures of sensitive installations, such as oil refineries.

Global Witness described the charges against Wykes as vague and demanded her unconditional release.

"We are worried ... because the charges are still not clear and the conditions for bail will not allow her to leave," said Gavin Hayman, a spokesman for the London-based group.

The British government has said it was discussing her case with Angolan officials.

Angola's government tends to take a dim view of foreign activists, especially when they are perceived to be meddling in Cabinda, a former Portuguese protectorate that is seen as critical to Angola's economic development.

Separated from the rest of Angola by a small strip of the Democratic Republic of Congo, Cabinda accounts for between 50 percent and 65 percent of the estimated 1.4 million barrels of oil produced each day in the southwestern African nation.

It was incorporated into Angola after independence from Portugal in 1975, a move that triggered a 31-year war with rebels who did not want to fall under the control of central government based in the capital Luanda.

An umbrella group of Cabinda rebel factions signed a peace agreement with the government in August, but tensions linger.

Angola, sub-Saharan Africa's second-largest petroleum producer after Nigeria, is frequently accused of having one of the world's most corrupt oil sectors, with large portions of revenue unaccounted for each year.

An estimated $4.2 billion "disappeared" from the Angolan treasury between 1997 and 2002, according to a 2004 report from the U.S.-based organisation Human Rights Watch.

Luanda, however, has refused to bow to Western demands that it make its economy more transparent, turning instead to China for the credit and loans to reconstruct after a devastating 27-year civil war that ended in 2002. (Additional reporting by Paul Simao in Johannesburg)

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