Fifteen children on board a hijacked school bus have been freed unharmed after a rescue operation by security forces in the country.

Police said that the children were rescued late on Thursday night in a forest, after being held for more than three days by gunmen demanding an initial $130,000 ransom for their release. By Thursday, Nigerian newspapers reported that the demand had been dropped to $2,600.

"All the 15 schoolchildren that were abducted on Monday have now regained freedom. They were rescued by a combined team of army and police security services late last night in the forest of Ogwe-Asa in Abia state," Jonathan Johnson, the police commissioner of Abia state on the edge of the Niger Delta, told the Reuters news agency.

He said that the children were now in the southern town of Aba, where they are thought to have  been held since being kidnapped. On Thursday, soldiers sealed off the town in a security sweep.  

The children are students of Abayi International School and are believed to be between three and ten years old. They may have been targeted because they come from wealthy families, Nigerian police have said.  

The kidnapping  was met with outrage in Nigeria, with Goodluck Jonathan, the country's president, describing it as "utterly callous and cruel".

Kidnappings are a common occurrence in the Niger Delta, a deeply impoverished region that hosts Africa's largest oil and gas industry. But the targets are often foreign oil workers and Nigerian adults, rarely children.

Three French oil workers were kidnapped from a drilling supply ship last week, and police in nearby Rivers state say five women were kidnapped two weeks ago by a gang believed to befrom Abia State. There has been no word on the fate of either group.

Source: Agencies