KANO, Nigeria: Multiple explosions rocked a highway checkpoint in Nigeria's second-largest city, witnesses said Wednesday, just over a month after a radical Islamist sect claimed an attack there that left at least 185 people dead.

The attacks raise fears that the radical Islamist sect is taking root in the northern city of Kano.

Resident Ali Garba, a 32-year-old bus driver, said he heard at least six explosions as he was preparing to head to the mosque for dawn prayers in a densely populated Kano neighborhood.

After that, he said, he heard gunfire for about two hours. By the time he left his house, the military had cordoned his neighborhood to prepare for searches, forcing him back into his home.

The attack occurred during curfew hours, he said, likely reducing its impact.

There were no casualties and four suspects were arrested during searches, said military spokesman Lt. Ikedichi Iweha who declined to comment further.

Boko Haram, whose name means "Western education is sacrilege" in the local Hausa language, is carrying out increasingly sophisticated and bloody attacks in its campaign to implement strict Shariah law and avenge Muslim killings in Nigeria, a multiethnic nation of more than 160 million people.

This year, the feared sect is blamed for killing at least 303 people, according to an Associated Press count. At least 185 people died in Kano last month in the group's deadliest assault yet.

The northern-based group has carried out attacks across Nigeria's mostly Muslim north but its attacks have been most persistent in the northeastern city of Maiduguri, the sect's spiritual home, where people live in constant fear of bombings and drive-by killings.

However, a series of attacks over the last month targeting military and police institutions - typical Boko Haram targets - in the much bigger city of Kano, about 380 miles (610 kilometers) away from Maiduguri, are raising fears that the group may be taking root there too.

Authorities have vowed to stop the sect, but the frequency, boldness and scale of its attacks have subdued many citizens' faith in the security forces' ability to suppress Boko Haram - a sentiment reinforced by a recent blunder.

In January a Boko Haram suspect escaped during a police-escorted prison transfer, but was then rearrested over a week ago. Kabiru Sokoto was accused of being involved in the Dec. 25 bombing of St. Theresa Catholic Church that killed at least 44 people in Madalla, a city just outside of Nigeria's capital of Abuja.

Nigeria's Police Service Commission announced Wednesday that the local police commissioner who ordered Sokoto's transfer, Hassan Zakari Biu, had been dismissed effective immediately.