MOMBASA: Gunmen in Kenya killed four people including a Muslim cleric in a drive-by shooting, police said Friday, an attack likely to inflame tensions in the key port city of Mombasa.

Radical preachers have said the killing was an “execution” by the police, claims that the security force has denied.

Slain cleric Sheikh Ibrahim Ismail was viewed as the successor to Aboud Rogo Mohammed, a controversial preacher accused of links to Somalia's Shebab insurgents, who was himself assassinated in a similar drive-by shooting in August 2012.

Rogo's killing sparked days of deadly rioting in Mombasa, with protestors accusing security forces of carrying out the killing; claims the forces had denied.

Police were expected to be on alert in case of any demonstrations later on Friday in Mombasa, Kenya's main port and a major tourist hub.

The deaths follow attacks last month by the Shebab, who launched a deadly assault on an upmarket Nairobi shopping mall, killing at least 67 people in a four-day bloodbath.

The Islamists have since threatened “rivers of blood” would flow in fresh attacks if Kenya does not pull its troops out of Somalia.

Local police chief Julius Wanjohi confirmed the killing of four men late on Thursday, and appealed to the public for information.

Salim Abdi was the only person in the car to survive the attack.

“There were gunshots and the vehicle veered off the road, I don't know how I walked out of the vehicle alive,” Abdi said. “All four others I was with in the vehicle died on the spot.”

A reporter at the scene said the car, with the windows shattered and the doors riddled with bullet holes, had smashed into the verge off the main coastal highway running north out of Mombasa.

Some bullet casings lay scattered around the car, suggesting that shots had been fired after the vehicle had stopped, while Ismail's bloodied body lay slumped on the backseat with his companions.

Like Rogo, Ismail preached at Mombasa's Masjid Musa mosque, which attracts some radical followers.

Rogo was on US and UN sanctions lists for allegedly supporting the Al Qaeda linked Shebab, including through recruitment and fundraising.

Another radical cleric, Abubaker Shariff Ahmed - known more commonly by his nickname “Makaburi” or “grave” in Swahili - spoke at the site of the attack, where he accused the police of the “outright execution” of his comrades.

“The police are killing people while saying it is a war against terrorism. This is a war against Islam,” Makaburi said, a former close colleague of Rogo who is also on a UN sanctions lists accused of recruiting and fundraising for the Shebab.

“These people have been executed.”