YOLA, Nigeria (AP) — It may take years to find all the Chibok schoolgirls kidnapped by the Nigeria-based Islamic extremist group Boko Haram, the country's defense minister warned Tuesday.

Boko Haram kidnapped 276 schoolgirls from a secondary school in the northeastern town of Chibok in April 2014. Some escaped and 21 were released last year after negotiations with Boko Haram, but 195 remain missing.

Nigeria's military is searching Boko Haram's hideouts in the Sambisa Forest, a vast area covering parts of three states in the northeast, Gen. Manir Dan Ali told Voice of America's Hausa language service.

He said even the United States needed a long time to find Osama bin Laden, the mastermind of the Sept. 11, 2001, attacks.

"It took the U.S. up to seven, eight, up to 10 years before they could get to bin Laden," he said. "We are continuing our campaigning in the Sambisa Forest in all its nooks and corners."

Ali spoke after Nigerians last week marked the third anniversary of the schoolgirls' abduction.

In 2014, Boko Haram had seized control of much of northeastern Nigeria but it has been driven back by a military campaign.

Failure to find the girls would translate into a victory for Boko Haram, said Sheikh Nuru Khalid, a member of a group that tries to encourage peace between Nigerian Muslims and Christians.

"We can never allow the terrorists to win the war. If they got (away) free with those girls, then they have relatively won the war," he said.

The government needs to address the psychological trauma suffered by victims of Boko Haram, human rights lawyer Abdu Bulama Bukar told VOA.

"Married women have been made single again. Kids have been orphaned. Homeowners are without shelter," he said. "Nigerians have been turned into refugees in their own homeland."