More than 200 schoolgirls abducted from their school dormitories by Boko Haram militants last year are not among the nearly 300 girls and women rescued in an army operation on Tuesday, an army spokesman said.

Nigeria's army said it had rescued 200 girls and 93 women on Tuesday during a military operation to wrest back the Sambisa Forest in the northeast from the militant group.

"The troops rescued 200 abducted girls and 93 women," Colonel Sani Usman told Reuters in a text message. They were not, however, from Chibok, the village from which more than 200 girls were abducted in April 2014, he said.

"So far, they (the army) have destroyed and cleared Sassa, Tokumbere and two other camps in the general area of Alafa, all within the Sambisa forest."

Boko Haram's action in Chibok caused an international outcry, and the group's six-year insurgency has seen thousands killed and many more abducted.

Diplomats and intelligence officials said they believed at least some of the Chibok girls were being held in the forest about 100 km (60 miles) from Chibok, although U.S. reconnaissance drones failed to find them.

The rescued girls and women will be screened on Wednesday to determine whether they had been abducted or if they were married to the militants, one intelligence source told Reuters.

"Now they are excited about their freedom," he said. "Tomorrow there will be screenings to determine whether they are Boko Haram wives, whether they are from Chibok, how long they have been in the camps, and if they have children."

Some of the girls were injured, and some of the militants killed, he said without giving more details.

The group was rescued from camps "discovered near or on the way to Sambisa," one army official said.

Nigerian forces backed by warplanes invaded the vast former colonial game reserve late last week as part of a push to win back territory from Boko Haram.

The group, notorious for violence against civilians, controlled an area roughly the size of Belgium at the start of the year but has since been beaten back by Nigerian troops, backed by Chad, Niger and Cameroon.

While the Nigerian army maintains the group is now hemmed in Sambisa Forest, militants have managed to launch attacks in the neighbourhood including chasing soldiers out of Marte town and an island on Lake Chad.