Sixteen students and workers have been freed after they were kidnapped by gunmen who attacked their university in northwest Zamfara state last week, university authorities said on Monday.

Security problems are one of the major challenges facing President Bola Tinubu, who is yet to spell out his plans to end the abductions, an Islamist insurgency in the northeast, gang and separatist violence in the southeast and farmer and herder clashes in the north central region.

Federal University Gusau said in a statement the attack had caused tension at the institution and students were worried about their safety.

"It is against this background that we appeal to students and staff to remain calm and go about their normal activities while the security agencies are doing their best to rescue the remaining students and other individuals that are still in captivity," the university said.

Fourteen students and two workers have been freed, the statement said.

The army, air force, police and state security agency are leading an operation to rescue the remaining victims after Tinubu instructed the security services to pursue the abductors.

Kidnappings of students, once a notorious tactic by Islamist militants to intimidate the population, have become a money-spinning industry for armed gangs demanding ransom payments.

(With input from Reuters)