|Opposition groups say more than 400 people have been arrested since Bahrain began a crackdown [GALLO/GETTY]
A Bahraini businessman who was a member of the country's leading Shia Muslim opposition group, Wefaq, has died in police custody, sources say.
There was no immediate reaction by state media to Kareem Fakhrawi's reported death and officials in the Arab Gulf kingdom were not available to comment.
Fakhrawi's was the fourth known death in police custody in recent days. Bahrain's government denies there is torture in Bahrain and says all such allegations will be investigated.
Mattar Mattar, a member of Wefaq, said Fakhrawi had died in police custody a week after he never returned home from a police station where he had tried to complain about his house being demolished by police.
"Either he was sick and didn't receive treatment or was tortured," Mattar said.
Wefaq said on Tuesday three Shia Muslim doctors and several staff from the education ministry had been arrested the day before, bringing the total number of detainees to 453.
"After these problems, many are afraid to contact us," Mattar said. "I estimate the real number is not less than 600. That's one in every 1,000 Bahrainis."
Bahrain says it has released 86 people held under martial law while "legal measures" are being taken against other detainees.
In another development, the daughter of a prominent Bahraini activist has begun a hunger strike in protest over the arrest of her father, husband, brother-in-law and uncle.
Zainab Al-Khawaja said on Monday that she would refuse food until her father Abdulhadi, who she said was beaten unconscious before being taken away, and other relatives were released.
Her father Abdulhadi al-Khawaja, a former president of the Bahrain Centre for Human Rights, an outspoken opposition organisation.
"I'm planning on doing this until the release of my four family members," Zainab Al-Khawaja told Al Jazeera from Manama via Skype on Wednesday.
Three of the men were detained following a police sweep on Zainab's house over the weekend, while her uncle was arrested three weeks ago.
The masked men who beat and arrested her family members were special security forces, she said, identifiable by their black uniforms.
Zainab al-Khawaja announced her hunger strike in a letter addressed to Barack Obama, the US president, posted on her blog Angry Arabiya.
"I chose to write to you and not to my own government because the Al-Khalifa regime has proven that they do not care about our rights or our lives," she wrote.
"I demand the immediate release of my family members. My father: Abdulhadi al-Khawaja. My husband: Wafi Almajed. My brother-in-law: Hussein Ahmed. My uncle: Salah al-Khawaja."
The US, whose Fifth Fleet is stationed in Bahrain, has offered only muted criticism of the government crackdown and analysts say it refrained from pressing Bahrain due to anxieties over interference from its rival Iran, just across the Gulf.
"If it wasn't for the American support [for the regime], I think the Bahraini people would have been much more successful in their call for democracy," she said on Wednesday.
Zainab al-Khawaja's announcement marks the first time an activist has gone on hunger strike since the Bahraini government began its crackdown on protesters on March 16.
Weeks of protests
Bahrain's Sunni Muslim rulers quelled weeks of protests led by mostly Shia demonstrators by deploying security forces throughout the capital, Manama, and calling in troops from neighbouring Sunni-led Gulf Arab states, including Saudi Arabia and the UAE.
Bahrain has also put two Iranians and a Bahraini on trial on charges of spying for the Revolutionary Guards, a key component of the Iranian government's security apparatus.
"They are accused of contacts with the Iranian Revolutionary Guard to give them military and economic information from 2002 to April 2010 ... with the intention of damaging the national interest," the Bahrain News Agency said.