Attacks by a Nigerian Islamist group Boko Haram have killed at least 935 people since the sect launched a violent campaign in 2009, including 250 this year alone, Human Rights Watch said on Tuesday.

"More than 935 people have been killed in some 164 suspected attacks" since Boko Haram launched its campaign of shooting and bomb attacks in July 2009, the New York-based global rights group.

"In the first three weeks of January 2012 alone, more than 253 people have been killed in 21 separate attacks," it said.

It said 185 police and residents were killed in coordinated attacks targeting mainly police stations in Kano -- the country's second largest city -- on January 20, Boko Haram's deadliest single operation.

The rights group urged the Nigerian authorities to put a stop to "this campaign of terror and bring to justice those responsible for planning and carrying out these reprehensible crimes."

"Boko Haram's attacks show a complete and utter disregard for human life," said Corinne Dufka, HRW's West Africa researcher.