The skulls and bones of at least 28 people have been recovered from suspected criminal camps in Nigerian forests.

Police in the south-eastern state of Abia are investigating the identities of the remains found in the Umuaku and Nneato forests on Saturday after a security operation was carried out in the Umunneochi area.

Police spokeswoman Maureen Chinaka said the suspects fled when police arrived.

The discovery is likely to revive concerns about kidnapping gangs operating in remote forests across parts of south-eastern Nigeria, where criminal groups have frequently targeted motorists, travellers and residents for ransom.

According to Abia State Police Command, the raids were launched following intelligence reports about suspected criminal activity in the forests.

Officers suspect the remains belong to kidnapping victims, although forensic and other investigations are ongoing to establish their identities and the circumstances surrounding their deaths.

"Upon arrival of the Command's tactical operatives at the camps, the suspects fled. The criminal camps were subsequently dismantled. A total of twenty-eight human skulls and bones, suspected to be kidnap victims, were recovered," Chinaka said in a statement.

Police said surveillance had been intensified in the area as officers sought to track down those who fled.

Abia state police commissioner Wilfred Afolabi said the operation was part of an ongoing campaign to dismantle criminal hideouts in the state.

Police have appealed to residents to report suspicious activity and security concerns as efforts continue to identify the victims and determine whether the remains are connected to unresolved kidnapping cases in the region.

Authorities have previously discovered decomposing bodies believed to be linked to kidnapping activities during security raids in Umunneochi.

Separately over the weekend, more than 80 people, mostly women, were seized in separate mass kidnappings in two states in the country's north.

In an attack on Sunday, nearly 50 farmers were abducted by gunmen in Niger State.

On Sunday, about 40 other women were kidnapped in the neighbouring state of Zamfara, according to two security reports seen by AFP and a local source.

Abductions for ransom have become a key source of income for criminals, including bandits and militant Islamists, in northern Nigeria.