ABUJA, Nigeria (AP) — Five soldiers and one police officer have been killed in an ambush in northwest Nigeria, the army said.

The attack occurred in Zamfara state on Monday, army spokesman David Adewusi said in a statement on Tuesday.

Authorities didn’t release details about who was responsible for the ambush, but referred to the attackers as “terrorists.”

“Despite the surprise of the ambush, the troops responded gallantly, engaging the terrorists and preventing further harm to nearby communities,” Adewusi said. “Regrettably, five soldiers and one police officer paid the supreme sacrifice during the encounter.”

The ambush followed successful operations in Zamfara last week, when three suspects were arrested and weapons recovered, he said.

Nigerian soldiers also rescued 62 hostages in a separate operation in the country’s northwest region on Wednesday.

Another army spokesman, Olaniyi Osoba, said that the hostages were released in the Munhaye Forest, a known hideout of notorious bandit leader Kachalla Alti, which is also located in Zamfara state.

“Efforts are ongoing to reunite the freed hostages with their families,” he said.

Northern Nigeria has been the hardest-hit part of the country, with a surge in kidnappings for ransom by gunmen across the northwest and north-central regions over the recent months, alongside an insurgency in the northeast.

Boko Haram, Nigeria’s homegrown jihadis, took up arms in 2009 to fight Western education and impose their radical version of Islamic law.

The insurgency now includes an offshoot of the Islamic State group known as the Islamic State West Africa Province or ISWAP. It has spilled into Nigeria’s northern neighbors, including Niger, killing about 35,000 civilians and displacing more than 2 million people, according to the United Nations.

Last month, the U.S. launched airstrikes in northern Nigeria, targeting IS, after allegations that the West African country failed to rein in attacks on Christians.