MAIDUGURI, Nigeria -- Islamic extremists in northeast Nigeria are turning their guns on elderly people, killing more than 50 this week in a new tactic that has instilled more fear in areas the militants call an Islamic caliphate.

Residents from five villages say people too elderly to flee Gwoza local government area are being rounded up and taken to two schools where the militants open fire on them. The villages are about 130 kilometres (80 miles) southeast of Maiduguri, the Borno state capital.

"What they are doing now is to assemble the aged people -- both men and women ... and then they just open fire on some of them," said Muhammed Gava, a spokesman for civil defence groups in the area. More than 50 people had been killed at Government Day Secondary School in Gwoza, he said.

A villager who had fled said more elderly people are being gathered and shot at Uvaghe Central Primary School. The villager spoke on condition of anonymity for fear of endangering his trapped parents.

Government officials did not immediately comment on the reports.

Nigeria's military said soldiers are patrolling "in search of terrorists" and "to verify abductions" Friday around the village of Gumburi, where witnesses say extremists kidnapped at least 185 people a week ago.

Nigeria's military and government have been criticized for their failure to rescue 219 schoolgirls kidnapped from a town near Gumburi in April.

In separate attacks Friday, witnesses said Boko Haram struck at Damagum and Mamudo towns in Yobe state, bombing government buildings, the police station and military barracks.

The extremists suffered a setback when they attacked soldiers guarding a power station in Borno state, according to an engineer who spoke on condition of anonymity for fear of reprisals. He said soldiers were warned in advance that the extremists were advancing and engaged the militants in fierce fighting that killed at least 70.

Extremists have killed thousands of people in a 5-year uprising that has driven some 1.6 million from their homes.

Associated Press writers Adamu Adamu in Damaturu, Nigeria, and Bashir Adigun in Abuja, Nigeria, contributed to this report.