A man push his bicycle walks past the ruins of a market outside the state police headquarters in Kano, Nigeria, last week.. Police said members of the radical Islamist group Boko Haram dressed in uniforms resembling those of soldiers and police officers when they launched their attack in Kano. At least 185 people died in the attacks.

Kano, Nigeria - Nigeria's Boko Haram Islamists have ruled out talks with the government and threatened new attacks in Africa's most populous country, rocked by an insurgency that has killed more than 200 already this year.

Residents in the northern city of Kaduna said the group, which has frequently targeted the police, may have struck again late Saturday when gunmen on motorcycles shot dead a policeman.

Police confirmed the killing early Sunday, but said the attackers were trying to steal the officer's motorcycle.

Kaduna resident Rabiu Tukur disputed that account.

“They did not make any attempt to take his motorcycle, which raised the fear that the attackers could be members of Boko Haram,” he said.

The group's deadliest ever strike came on January 20, north of Kaduna, in Nigeria's second city of Kano, where a coordinated set of gun and bomb attacks killed at least 185 people, highlighting the Islamists' renewed strength.

Heavily criticised amid the escalating violence, President Goodluck Jonathan urged the group to enter dialogue in a media interview this week.

But Jonathan's call for talks was “not sincere”, Boko Haram spokesman Abul Qaqa told journalists by telephone in the north-eastern city of Maiduguri, regarded as the group's stronghold.

“We don't think dialogue is possible under the current situation,” he added.

If captured members of the group were not released, it “will launch attacks in Sokoto similar to the big Kano attacks”, Qaqa warned.

Sokoto is a north-western city which is the capital of a state of the same name.

Kano, Nigeria's second city and north of Sokoto, had escaped the worst of Boko Haram's violence, but since the deadly January 20 attacks the mainly Muslim northern hub has been put on edge.

The military and police guarded the city's churches on Sunday, and worshippers were frisked before being allowed to enter, according to an AFP reporter.

Crowds were thin and services ended earlier than usual because of security concerns, worshippers said.

In a leaflet distributed around the city overnight, Boko Haram urged the city's residents to persevere as the group continues its campaign against Nigeria's security forces.

Boko Haram is aware of “the atmosphere of inconvenience our operations have thrown people into,” the leaflet said.

The document's content could not be independently verified, but was described as a message from purported Boko Haram chief Abubakar Muhammad Shekau.

“You should ... persevere with the difficult situation the struggle for the entrenchment of an Islamic system puts you in and seek reward from God by supporting it,” it said.

Boko Haram's intensified violence has shaken Africa's top oil producer, which is divided between a mainly Muslim north and mainly Christian south.

But as its attacks escalate, the group's specific aims remain largely unclear.

It has previously said that it wants to create an Islamic state in Nigeria's deeply impoverished north.

Top Nigerian politicians have denied that the Boko Haram insurgency is being fuelled by religious tensions, linking the group to like-minded external Islamist groups such as Al-Qaeda.

Many analysts however doubt the strength of those links and say Boko Haram remains focused on a domestic agenda and is boosting its strength by exploiting religious tension within Nigeria.

The group launched an uprising in 2009 that was put down by a brutal military assault.

It fell dormant for about a year before re-emerging in 2010 and is now believed to have a number of different factions, including a hardcore Islamist cell. - Sapa-AFP