A Bahraini man died overnight after being tear-gassed, the opposition said on Thursday, disputing the government version that he died of a blood disorder.
Jawad Marhoun, 36, died from "excessive exposure to tear gas from a canister tossed into his parents' home on September 10," the main Shiite opposition group Al-Wefaq said in a statement.
Marhoun was rushed to hospital early on Tuesday "after his condition worsened," and he died at Manama's central Salmaniya hospital on Wednesday evening, it said.
The government, which cracked down on pro-democracy protesters in mid-March, said in a statement Marhoun died from "acute respiratory" problems as a result of sickle cell disease.
In April, the government said that two other activists died from the blood disorder while in custody.
Marhoun's is the second disputed death in less than a month.
On 31 August, Ali Jawad Ahmed al-Sheikh, 14, died in the Shiite village of Sitra during a protest after prayers commemorating the beginning of the Muslim holiday of Eid al-Fitr.
The opposition said Sheikh was fatally wounded when he was struck in the face by a tear gas canister fired by security forces.
The government said the teenager died of blunt trauma to the back of the neck that could not have been caused by a rubber bullet or tear gas.
The deaths come ahead of parliamentary elections scheduled for September 24.
The opposition has boycotted the elections and wants democratic reforms in the tiny Gulf kingdom where a Sunni monarchy has ruled over a majority Shiite population for decades.
Matar Matar, a senior Al-Wefaq member and former MP facing trial for allegedly calling for regime change and spreading rumours linked to the pro-democracy protests, called the situation in Manama "tense."
"Spontaneous demonstrations are breaking out every night in the Shiite villages, and every night the security forces are responding with tear gas," Matar told AFP.
Security forces in the archipelago were aided in the March crackdown on protesters after being backed by troops with tanks from neighbouring monarchies.
Authorities said 24 people were killed in the unrest, including four policemen. The opposition put the toll at 30.