Suspected Islamists kill 2 Nigeria police at checkpoint

* Boko Haram commander arrested in Maiduguri

* Islamists remain Nigeria's top security threat

KANO, Nigeria, Jan 14 (Reuters) - Two Nigerian policeman were killed on Monday at a checkpoint in northern Kano state by suspected militants from the Islamist sect Boko Haram, the government said.

After a surge in violence around the turn of the year, there have been fewer attacks by the Islamist militants, although they remain the biggest security threat to Africa's top oil producer.

Captain Ikedichi Iwewha, spokesman for joint military and police forces in Kano, confirmed the checkpoint attack and said two civilians who were praying by the roadside were wounded.

"They numbered over five and opened fire on police. Two people are being treated for gunshot wounds," he said, adding that two militants were also wounded but managed to flee.

Boko Haram, based loosely on the Afghan Taliban, killed hundreds last year in a campaign to impose sharia, or Islamic law, on Nigeria, a country of more than 160 million people split roughly equally between Christians and Muslims.

Boko Haram's violence remains focused mostly on security forces in the northeast, although its attacks have spread across the north and to the capital Abuja.

Lieutenant Colonel Sagir Musa said a senior Boko Haram commander, Mohammed Zingina, was captured on Sunday in Maiduguri in the northeast, where the sect's headquarters lie. The government blames Zingina for several suicide bombings.

The government has promised rewards for information on some Boko Haram members that could lead to their arrest. In Zingina's case the bounty offered was 25 million naira (${esc.dollar}160,000). (${esc.dollar}1 = 156.4250 naira) (Reporting by Chukwuemeka Madu; Additional reporting by Ibrahim Mshelizza in Maiduguri; Writing by Tim Cocks; Editing by Tom Pfeiffer)