Four American hostages seized weeks ago in Nigeria's restive southern oil heartland were publicly handed over to authorities on Wednesday.

As journalists looked on, a judge who mediated in the dispute escorted the four men taken May 9 to the governor's offices in southern Rivers State where he handed the liberated hostages over to authorities. U.S. embassy officials weren't immediately available for comment.

Some 200 foreign workers have been kidnapped since armed militants stepped up their attacks against oil companies and the government in late 2005. Most have been quickly released for ransom.

Growing lawlessness, including armed attacks, in the oil-rich Niger Delta have cut about a quarter of exports from Africa's leading oil producer. The impoverished region has nearly all of Nigeria's oil, and most inhabitants want an increased share of revenue.

In his inaugural speech Tuesday, President Umaru Yar'Adua appeal for an immediate end to violence in the region of swamps, creeks and mangrove forests. The largest militant group said it would consider the overture.