Amnesty International has called for an investigation into what it says is the misuse of tear gas by Bahraini security forces.
The organisation says that more than a dozen deaths may have resulted from the heavy use of tear gas in residential areas.
Police are struggling to contain a growing wave of protests in the gulf island kingdom.
The most recent death attributed by activists to tear gas was on Wednesday.
Saeed Ali Hasan al-Sakri, 65-years-old, is said by his family to have collapsed after a heavy volley of tear gas was unleashed near their home in a Shia village on Tuesday.
Shia in Bahrain have long complained of discrimination at the hands of the Sunni ruling family. Pro-democracy protesters briefly occupied a prominent traffic roundabout in February of last year.
Since being driven out of Pearl Roundabout in mid-March, mainly Shia demonstrators have continued to agitate against the government.
An independent panel of human rights experts was appointed by King Hamad after growing international condemnation of human rights abuses.
The report published in November confirmed excessive use of force and systematic torture of prisoners in detention by security forces.
But according to both activists in the country and international human rights organisations little has been done to curb the police.
Eye witnesses have told the BBC of stun grenades and tear gas canisters being fired into houses in violation of international standards that Bahrain has signed up to. Amnesty International has called for an investigation into the deaths, adding: "The security forces must be instructed on how to use tear gas in line with international policing standards."
Amnesty International says that in some cases death seems to have resulted from an adverse reaction because of pre-existing health conditions such as asthma.
Rising death toll
This week, four deaths have been attributed by activists to the actions of the security forces.
That brings the death toll since unrest began last year to at least 50, including four security officers.
In addition to Mr Sakri, activists say that 24 year old Abbas Jaffar al-Shaikh died Wednesday of complications after being hit in the back with birdshot nearly two months ago.
A spokesperson for the government said he was being treated for cancer when he died.
The spokesperson said that Mr Sakri had died after a fall in his bathroom, adding "the Public Prosecutor ordered forensic examination to test blood but no results have been released yet".
Muntadher Saeed Fakhr was said by the Ministry of the Interior to have died in a traffic accident on Wednesday afternoon. Activists say he was deliberately run off the road by police.
The BBC has seen a picture that is said to be of Mr Fakrh handcuffed and bleeding in a police vehicle.
Mohamed Ibrahim Yaqoob died in hospital late Wednesday night. The BBC has seen two videos, one that appears to show the 19-year-old being chased and run down by a police vehicle in the village of Sitra.
The second released by the police shows him in custody in a police car, apparently unhurt.
A source told the BBC that Mr Yaqoob was first taken to a police station, and held for two hours before being admitted to hospital. The source says he died of internal bleeding four hours later.
The Ministry of Interior is responsible for the security forces.
On its website it says that Mr Yaqoob died of what it called "natural causes" after being taken to Salmaniya Hospital immediately after informing arresting officers that he suffered from sickle cell anaemia.
But the BBC has seen photographic evidence of cuts and bruises on his body.
The ministry has not yet commented on the call by Amnesty International to investigate deaths said to be related to the use of tear gas by its security forces.