The insurgents allegedly smuggled the devices through the porous Lunga Lunga border before assembling them within Mombasa.
Mombasa CID boss Henry Ondiek said security had been beefed in key installations among them the Moi International Airport and shopping malls.
The operation in Mombasa was followed by warnings by the Ugandan Government that Al Shabaab insurgents were planning to use fuel tankers as bombs to carry out attacks.
Ugandan police chief Kale Kayihura ordered his officers to escort all fuel tanks from the Kenyan border to various parts of Uganda, as one of the measures to foil any terror attacks.
Both Uganda and Kenya are key contributors of troops to the African Union force fighting Al Shabaab in Somalia, and the Islamists have carried out major attacks in both countries in retaliation in the past.
