PORT HARCOURT (AFP)--Nigeria is losing $180 million in revenue monthly following the closure of a key offshore Shell gas plant in the volatile Niger Delta, a Royal Dutch Shell PLC (RDSA) spokesman said Thursday.

Precious Okolobo told reporters in Port Harcourt that the Anglo-Dutch oil giant was making efforts to repair the Soku plant, which was shut down on Nov. 27, 2008 after its pipelines were sabotaged.

The Soku plant, located in the swamps of the southern Rivers State, accounts for some 40% of the gas feed to Nigeria Liquefied Natural Gas Ltd.

NLNG supplies liquefied natural gas to markets in Europe and the United States.

After the Soku pipelines were vandalized, Shell declared a force majeure on NLNG.

Shell has a 26% stake in NLNG and the state-run Nigerian National Petroleum Corporation holds 49%. Other significant shareholders in the gas venture are France's Total (TOT) and Agip of Italy.

Shell has been a regular target of attacks by militants in the Niger Delta over the past three years, forcing it to shut down some facilities and several times defer contractual obligations to clients.

Unrest in the Delta has reduced Nigeria's oil output by more than one quarter, putting pressure on crucial export earnings.

Daily oil production in Nigeria currently stands at around 1.78 million barrels, against some 2.6 million barrels in 2006.