Nigeria police guard phone masts after attacks

* Suspected Islamists blow up and set fire to masts in north

* MTN, Etisalat, Airtel all targeted

* Seven members of Boko Haram killed in Maiduguri - military

ABUJA, Sept 7 (Reuters) - Nigerian police officers were guarding telecoms equipment across the country following a spate of attacks on phone masts in the north, the head of the police force said on Friday.

Suspect Islamist militants have blown up, burnt and torn down masts belonging to MTN, Airtel, Etisalat and other mobile groups over the past two days.

Boko Haram, Islamist militants who have killed hundreds this year in the largely Muslim north, has not claimed responsibility. Sources close to the group said its members were concerned they were being traced through their mobile phones.

The group, which wants to carve out an Islamic state, also targets security installations, government offices and churches. Its low level insurgency has lasted more than two years.

The military joint task force for the northeast said on Friday its personnel had killed seven Boko Haram members and arrested 13 more on Wednesday after a gunbattle in northeastern city of Maiduguri, the group's heartland.

The Inspector-General of Police had ordered all regional forces to set up special units "to ensure the safety of telecommunication equipment and installations", a statement from his office said.

In the latest reported attack, gunmen on motorbikes used high-calibre explosives to destroy masts belonging to MTN, Etisalat and privately owned companies Globacom and Visafone in the north's biggest city Kano on Thursday, police said.

Attackers also wrecked more than a dozen masts in Kano and Maiduguri on Wednesday.

A spokeswoman for MTN Nigeria said by email on Friday that the operator was focusing its efforts on restoring services to customers in the areas hit by the sabotage.