Speaking to journalists, Bosso said they had tracked the kidnappers.

"The drone actually showed us exactly their location. But our predicament is that with the intel we have... the camp is mined with IEDs [homemade bombs]," he said.

Bulldozers and armoured vehicles are being deployed as police prepare for a rescue operation.

Kidnapping for ransom is a major security problem in Nigeria, involving both criminal gangs and armed groups.

The abduction in Imo state has caused widespread concern, with mass kidnappings less common in southern Nigeria than in some parts of the north.

Paying ransoms is illegal and authorities have repeatedly warned families against doing so, but relatives of kidnapped people are often under pressure to do so to secure their release.

The latest abduction highlights the risks faced by young people travelling across Nigeria to do their national youth service and has renewed calls for reforms.

The NYSC has previously said it would not deploy members to areas considered high-risk because of violence or the threat of abduction. Most parts of south-eastern Nigeria have not previously been classified as high-risk areas.

In the south-east, some previous abductions have been linked to separatist groups, including the Indigenous People of Biafra (Ipob).

Authorities have not linked the current abduction to any group.

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