An unknown number of university students have been kidnapped in the south-eastern Nigerian state of Abia.

The group was abducted on Wednesday, the same day that 29 students seized last month in the north-western state of Kaduna were released, reportedly after the payment of a ransom.

The authorities in Umuahia, the state's capital, say the students of the Abia State University Uturu were moving in a minivan on Wednesday evening when they ran into the armed gang. They were kidnapped alongside other travellers.

Two of the students escaped from the kidnappers while others were still being held at an unknown location, John Kalu, the state government's information commissioner, said.

Such abductions have become common in parts of Nigeria.

On Thursday, Nigeria's military chiefs appeared before parliament to be questioned about the nationwide security challenges.

President Muhammadu Buhari is under increasing pressure because of the surging violence by criminal gangs, Islamist militants and separatists.

Parliament has urged him to declare a nationwide state of emergency.