Police in Kenya's coastal city of Mombasa raided two mosques and arrested more than 100 people about a day after taking 251 people into custody during a swoop on two other mosques in the port city.

Security officers say they arrested 109 people following raids on Swafaa and Minaa mosques in the Kisauni area Tuesday night.

They seized several petrol bombs, hand grenades and assorted ammunition.

Earlier raids on the Sakina and Musa mosques in Mombasa's Majengo area ended with one person dead, 251 youth in custody and some eight grenades and a pistol among recovered items.

Four people were stabbed and killed in Mwandoni, Kisauni Monday night in attacks believed to be reprisals for the raids. Police are cracking down on radicalised youth sympathetic to Somalia's Al-Shabaab terrorists who have in recent months forcefully taken over control of several mosques in the coastal area.