Nigerian security forces said on Sunday they were searching for Islamist militants behind a coordinated attack in the north that killed at least 65 people, as residents still in shock demanded the government do more to protect them.

The Boko Haram Islamist sect has claimed responsibility for multiple gun and bomb attacks in the city of Damaturu Friday in its deadliest attack yet, which left bodies littering the streets and reduced police stations, churches and mosques to smouldering rubble.

We are ready for them, we are going to comb every place in the state to until we find and deal with them. Our men are ready, Suleiman Lawal, police commissioner for Yobe state of which Damaturu is the capital, told Reuters.

Sunday suspected Boko Haram militants shot dead an off-duty police officer as he returned from prayers to celebrate a Muslim holiday in Maiduguri, the group's main base, Borno state police commissioner Simeon Midend told Reuters.

Lawal gave the official death toll as 53. An emergency relief agency that counted bodies in the morgues gave a toll of 65 -- 63 from the Damaturu attack and another two from a strike on a neighboring village, Potiskum.

Residents still in shock questioned how the gunmen were able to take over the city and wreak havoc with apparent ease.

I am a Muslim but what is happening in Nigeria now is unacceptable. President Jonathan and his security chiefs should take control of the situation. We are tired of these terrorist acts, said Abdulgafar Bello, 48, a market trader.

The U.N. Security Council overnight condemned in the strongest terms the terrorist attacks that occurred in Damaturu and Potiskum, and urged global measures to combat terrorism.

Boko Haram, whose name means Western education is forbidden in the Hausa language, is growing in sophistication, and the increasing audacity and deadliness of its attacks are becoming a major security headache for President Goodluck Jonathan's administration.

Friday's violence also included a spate of bomb attacks in Maiduguri. The group has also hit the capital twice this year.

GROWING MILITANT THREAT

Boko Haram claimed responsibility for a bombing of the U.N. Nigeria headquarters in Abuja that killed 26 people in August.

The U.S. embassy issued a warning to citizens Sunday to avoid hotels in the Nigerian capital, which it said could be targeted in the next few days.

The U.S. Embassy has received information that Boko Haram may plan to attack several locations and hotels in Abuja (this week) ... Targets may include the Nicon Luxury, the Sheraton Hotel, and the Transcorp Hilton Hotel, it said in a statement.

President Jonathan rarely comments on frequent attacks in the north, but Saturday he said in a statement he had directed security agencies to ensure the arrest of perpetrators of these heinous acts, and assures Nigerians that all necessary will be done to ensure safety of lives ...

Many Nigerians were unimpressed.

How can the president use the same cliche to address another mass murder of Nigerians he swore an oath to protect? Why not declare war on Boko Haram? What is wrong with his executive powers? What is wrong with Nigeria? wrote a blogger called Ken on the website of Nigeria's This Day newspaper.

But efforts to make war on Boko Haram in the past have done little to quell the insurgency and heavy-handed police tactics in the northeast have radicalised youths against the state -- creating a fertile breeding ground for more militancy.

Ultimately, Nigeria may have to address the poverty and sense of alienation in the remote, semi-arid north, which feels increasingly left out of the economic growth enjoyed by the oil-rich south.

A state-sponsored committee in September urged establishing a dialogue with Boko Haram, an idea reiterated Sunday by the governor of Borno, the worst affected state, Kashim Shettima.

Governor Kashim ... calls on the aggrieved sectors of our society to eschew the violent expressions of their grievances ... and dialogue with the government, with a view to amiably resolving whatever their grievances may be, he said.

Residents said life was slowly returning to normal in Damaturu, as Muslims there slaughtered sheep to celebrate Eid al Adha, the Islamic festival of sacrifice.

Nigeria, a country of 150 million people split nearly evenly between Christians and Muslims, is mostly peaceful, but growing militancy in the north and violence in the ethnically and religiously mixed Middle Belt are an increasing worry.

(Reporting by Mike Oboh; writing and additional reporting by Tim Cocks in Lagos; editing by Philippa Fletcher)