Armed police patrolled the streets of Kenya's port city Mombasa Wednesday after a prominent radical Muslim cleric assassinated overnight was buried as martyr.

But Kenya's second city - a key transport hub for East Africa and a popular tourist destination - was reported calm in the morning, with the slain cleric's mosque broadcasting appeals for restraint among his supporters.

The cleric Abubaker Shariff Ahmed, was a vocal supporter of Osama bin Laden, and was on a UN sanctions lists accused of being a "leading facilitator and recruiter of young Kenyan Muslims for violent militant activity in Somalia," and of having "strong ties" with Shebaab leaders.

Better known as Makaburi or "grave" in Swahili, he had described last year's attack on the Westgate shopping mall in Nairobi, which was claimed by Somalia's Al Qaeda-linked Shebaab rebels, as "100-percent justified."

An AFP reporter in the city said Muslim clerics' appeals for calm rang out from loudspeakers at Makaburi's mosque throughout the night. Similar calls were also made on local radio stations.

Senior police officer in Mombasa Richard Ngatia confirmed Makaburi had been killed by "unknown assailants."

Previous killings of clerics have sparked deadly riots, with supporters clashing with the police.

There were initial angry scenes outside the police station where the body had been taken, and police fired into the air to push back furious supporters of the cleric.

But while there was a tense atmosphere and police and security forces had deployed in large numbers - including putting extra armed guards around key churches in flashpoint areas - Mombasa was calm.

"We condemn this extra-judicial killing, and we are far from happy at the security situation here ... these killings have to stop," said Sheikh Muhdhar Khitamy, regional chairman of the Supreme Council of Kenya Muslims.

"However, we call for calm and for people not to react with violence," he added.

At the same time, Kenyan police have arrested more than 650 suspects a day after six people were killed in bomb attacks in the capital Nairobi, the interior minister said Tuesday, in a crackdown on suspected Islamist insurgents.

"This act of cowardice perpetrated against innocent and peace-loving Kenyans who were going about their normal activities is barbaric," Interior Minister Joseph Ole Lenku said in a statement.

"So far 657 suspects have been apprehended," he added.

AFP