ABUJA, Nigeria (AP) — Nigeria’s navy has seized a foreign ship and detained 27 foreigners who are charged with operating illegally on Nigerian waters and attempting to export crude oil without clearance, a senior official told The Associated Press on Wednesday.

The foreigners are being held on court orders following their arraignment in a local court in the oil-rich Niger Delta region, according to Nigerian Navy spokesman Commodore Adedotun Ayo-Vaughan.

Some of the foreigners were arraigned on Tuesday after being charged with an “attempt to deal in export (of) crude oil without license or authorization.” They included 16 Indians and nationals from five other countries including Sri Lanka and Poland, Ayo-Vaughan said.

Foreigners accused of illegally operating in Nigeria’s maritime territory have been arrested in the past and analysts say they often work in connivance with local residents.

Nigeria loses an estimated 470,000 barrels of crude oil per day to chronic theft and pipeline vandalism, according to experts. Security forces have in recent months intensified a clampdown on culprits and the intelligence required to uncover their activities “is being sustained,” said Ayo-Vaughan.

In the latest incident, a ship registered in Marshal Island with a capacity to carry 3 million barrels illegally entered Nigeria’s waters on August 7, officials said.

Nigerian authorities said the captain confirmed that “his vessel was without relevant clearance to operate in the field” but subsequently “declined” a request to follow a Nigerian Navy ship. Instead, officials said it made “a false piracy attack call” and “engaged full speed southwards towards the Sao Tome and Principe maritime area in a bid to evade arrest.”

“We are still keeping good surveillance as well as presence by the patrol of our ships in the waters and we also have a subregional and international partnership to continue to uncover this kind of criminality of international dimension,” said Ayo-Vaughan.