Shiite villages frequently witness clashes between security forces and protesters demanding Bahrain's ruling Sunni Khalifa family to surrender its grip on all key cabinet posts in favour of an elected government.
The bombs exploded as "security forces were confronting acts of sabotage, blocking of roads and attacks with molotov cocktails," police said in an English-language statement published by the official BNA news agency.
There were no reports of casualties but an investigation is underway, it said.
They "used poisonous gases to attack... A religious establishment" where mourners had gathered causing "injuries and suffocations" among residents.
Arab Spring-inspired protests in Bahrain began in mid-February 2011 and were met by a crackdown a month later. But mostly young protesters still take to the streets in Shiite villages surrounding Manama, often clashing with security forces.
The International Federation for Human Rights says at least 89 people have been killed since the uprising broke out three years ago.