Nigeria ? Four American oil workers abducted three weeks ago in Nigeria’s restive oil region were released Wednesday.

As journalists looked on, a judge who mediated in the matter escorted the four men to the governor’s office in southern Rivers State and turned them over to authorities. U.S. Embassy officials weren’t immediately available for comment.

The men’s identities were not released. Chevron Corp. reported May 9 only that the men had been seized when their work boat was stopped by gunmen armed with assault rifles and rocket-propelled grenades.

Some 200 foreigners have been kidnapped since armed militants stepped up attacks on the oil industry and the government in late 2005, pressing their demand that more oil revenue be put into the impoverished Niger Delta. Most hostages have been quickly released for ransom.

Growing lawlessness in the oil-rich region has caused a 25 percent decrease in petroleum exports from Nigeria, Africa’s leading oil producer.