Nigerian police are conducting 24-hour surveillance of all telecom installations after the terrorist group Boko Haram claimed responsibility for a recent spate of attacks on mobile phone towers in the northern reaches of the country.

Boko Haram has accused the telecom companies of breaking their "ethical obligations" and helping security agencies spy on its members.

So far, the group's activities have affected nine companies, although it is unclear how much damage has been caused. The cost of a communications tower can be more than $1 million, the BBC News reported.

Nigerian police chief Mohammed Abubakar assured telecom companies that special units would closely monitor all installations.

"With that guarantee, we will continue to provide services, so we do not intend to discontinue services," Gbenga Adebayo, chairman of the Association of Licensed Telecom Companies of Nigeria, told BBC News.

Boko Haram is a militant Islamist sect that aims to implement sharia law across Nigeria. It has claimed responsibility for a series of attacks on government and civilian targets, killing more 935 people since 2009, according to Human Rights Watch.

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