MOMBASA, Kenya - At least seven policemen have been injured, four critically and one feared dead, in another grenade attack in Kenya's coastal city of Mombasa on Wednesday night.

Policemen secure the scene of an explosion in Kenyan coastal city of Mombasa, Aug 29, 2012. [Photo/Agencies]

Divisional police commander Kipkemboi Rop confirmed the incident which took place at Mwembe Tayari area of Mombasa that also left the person who hurled the grenade at the police vehicle critically injured during the shootout with police.

"I can confirm that seven police officers were injured when a man hurled a grenade at the LandCruiser police vehicle which was patrolling in Mwembe Tayari. Four of the officers are in critical condition while the person who threw the grenade has also been shot and is in critical condition," Rop told journalists at the scene of the incident.

Rop said the grenade was hurled from top of a tall building by two youths, prompting a shootout with the police where one of the boys was shot and is critically injured.

"We have rushed the injured police officers to the hospital. We also managed to arrest the youth who hurled the grenade. This was a coward act but we are winning this war," Rop said as the police sealed off the area to allow bomb experts to take the samples for further analysis.  

The riots that began on Monday and continued throughout Tuesday after unknown thugs assassinated controversial Islamic preacher Aboud Rogo in the broad daylight.

Eight churches were attacked. One was set on fire and one was looted of electrical equipment. Shops and two cars were set on fire and burning tires placed in the road in several areas of town.

Police engaged in running battles with rioters, firing tear gas and rubber bullets. More security officers were brought in as reinforcements.

The authorities have so far arrested over 30 people in connection with the riots while more than 20 youths were charged in court on Wednesday.

Relative calm had returned in the coast city of Mombasa early Wednesday after the violent protest.

Heavy presence of security personnel comprising officers from the Kenya Regular Police, General Service Unit and Administration Unit were patrolling major highways ahead of the arrival of Kenyan President Mwai Kibaki who is due in the city on Thursday.

Regional police commander Aggrey Adoli confirmed that isolated cases of chaos were reported early in the day at Majengo area and Bondeni areas but were thwarted by police.

"We have restored sanity in the city and I am appealing to locals to maintain peace and calm as we continue with our investigation," Adoli said.

The youths who were charged in Mombasa court for engaging in protests and unlawful activities were denied bond when they appeared before Mombasa resident Magistrate Elvis Michieka where they pleaded not guilty.  

The police said they are also looking for Muslim cleric who is behind the violence at Majengo area where Rogo enjoyed support.