* Helicopter gunship battle kills 17 militants, one soldier
* Security forces destroy Islamist training camps
* Persistent violence casts further doubts on ceasefire
* Camp attacks follow Boko Haram raids on police stations (Adds details)
By Ibrahim Mshelizza
MAIDUGURI, Nigeria, Feb 1 (Reuters) - Nigerian authorities said on Friday security forces backed by helicopter gunships killed 17 militants and destroyed two training camps belonging to Islamist sect Boko Haram, one in a forest and one in a game reserve.
Lieutenant Colonel Sagir Musa, spokesman for joint military and police forces in Borno state, said one soldier had also been killed in the firefights, which cast fresh doubt on a ceasefire declared by one purported Boko Haram commander this week.
"The camp was properly ... fortified and had training facilities, an armoury, accommodation, a drug store, kitchen, vehicle holding area, latrine and water points," Musa said. It was not clear which of the two camps he was referring to.
"The camp was used to conduct training and carry out recent attacks, killings and bombings," he said. Borno state is the sect's headquarters and the worst affected by the insurgency.
There was no immediate reaction from Boko Haram, whose militants have destabilised Africa's top energy producer and raised fears it could become a base for the operations of al Qaeda-linked Islamist groups in the Sahara.
Sheik Abu Mohammed Ibn Abdulazeez declared a unilateral ceasefire on Monday, urging members to halt attacks that have killed hundreds since the group launched an insurgency against the government in 2009.
Nigerian authorities welcomed the move but said they would not cease military operations to maintain security.
Violence by suspected sect members has persisted, raising doubts about the commander's authority. Gunmen killed at least five police in two attacks in northern Nigeria on Thursday.
Abdulazeez claimed to be speaking on behalf of Boko Haram leader Abubakar Shekau, who neither publicly backed nor denounced the commander when he called for dialogue twice in November last year.
But after a week of violence, Abdulazeez looks increasingly like a faction leader who may not hold much sway over the disparate bands of militants killing in the name of Boko Haram.
On Wednesday, gunmen shot dead a security guard at the entrance to the university of Maiduguri, capital of Borno.
Musa said after the attacks on Friday Nigerian forces had recovered a variety of automatic rifles, a rocket propelled grenade kit, and more than 2,500 rounds of ammunition.
President Goodluck Jonathan has highlighted links between Boko Haram and Saharan Islamists including al Qaeda in the Islamic Magreb as a reason for joining efforts by allied French and West African forces to fight them in Mali. (Additional reporting by Isaac Abrak in Kaduna; Writing by Tim Cocks; Editing by Louise Ireland)