The authorities in Niger state in central Nigeria have ordered the immediate suspension of all mining activities.

It comes days after gunmen launched a devastating attack on a mining site, kidnapping at least four Chinese miners and killing over 20 members of the Nigerian security forces.

Those abducted remain in captivity.

Niger state government fears some of the privately-run gold and other mines may harbour criminals, and intends now to screen mining sites state-wide.

The federal government also believes proceeds from mining may be funding some of the violent kidnapping gangs currently rife in Nigeria.

Nigeria is struggling to curb a wave of kidnappings for ransom by armed gangs - some of which have at times teamed up with Islamist extremists.

Mining activities have been suspended in some areas in the past but the measure failed to end the kidnapping crisis.