(CNN) -- A human rights advocate was reported missing in Bahrain on Saturday after masked security guards beat him unconscious in the middle of the night and carried away him and two sons-in-law, according to his daughter and a human rights group.
Missing is Abdulhadi Al-Khawaja, former president of the Bahrain Center for Human Rights and a former protection coordinator with the International Foundation for the Protection of Human Rights Defenders' Front Line.
He was taken away after security agents stormed the home of another daughter where he was staying in Manama, Bahrain, at 3 a.m. Saturday, according to Front Line.
The Bahraini government didn't have an immediate comment.
However, on Saturday, Bahrain's Ministry of Interior reported the deaths of two protesters while being held in custody.
Ali Isa Saqer, 31, died at a detention center on Saturday, according to the general director of Muharraq Governorate Police. Saqer was being held on charges of attempted murder of policemen while trying to run them over with his car on March 13.
Authorities said Saqer was creating chaos at the detention center, and when security forces sought to subdue him, he resisted them and sustained various injuries in the process. He was sent to the hospital, where he later died.
The prosecutor's office and medical examiner were investigating the cause of the death, authorities said.
Also on Saturday, Zechariah Rashid Hassan, 40, who was being held since April 2, was found dead in a detention facility, and an autopsy confirmed the cause of death was sickle cell disease, authorities said. Hassan was charged with inciting hatred against the government, spreading false news and calling for an overthrow of the government, authorities said.
Meanwhile, the case of missing Abdulhadi Al-Khawaja has left human right groups concerned.
"Front Line is gravely concerned for the physical and psychological integrity of Abdulhadi Al-Khawaja and believes that he faces a high risk of torture and ill-treatment in detention," the organization said in a statement.
"Front Line believes that Abdulhadi Al-Khawaja's arrest and detention is directly related to his legitimate and peaceful work in defense of human rights," the statement said.
Daughter Maryam Al-Khawaja of Rhode Island, who's the head of foreign relations for the center, told CNN that her father was staying with his three daughters, wife and three sons-in-law.
Security forces first searched his apartment, and when they found it empty, they went to the home of his cousin, Habib Alhalwachi, who was arrested and then released, according to the daughter and Front Line.
When the masked officers arrived at the daughter's apartment, they assaulted Al-Khawaja and son-in-law Mohammed Al-Masqati, who's also president of the Bahrain Youth Society for Human Rights, according to Front Line. One of the officers spoke English and no Arabic, the group said.
The Bahraini officers dragged Al-Khawaja down a staircase, and five officers beat him, despite his cries that he couldn't breathe, according to Front Line and Maryam Al-Khawaja.
When daughter Zainab Al-Khawaja tried to intervene, security forces dragged her upstairs and threw her inside her apartment, Maryam Al-Khawaja said. Her sister suffered minor injuries, she said.
Al-Khawaja and his three sons-in-law were taken to a lower apartment in the building where they were ordered to lie on the floor and were beaten severely by police, Front Line said.
Al-Khawaja lost consciousness, the human rights group said.
Police took Al-Khawaja and two sons-in-law, Wafi Almajid and Hussein Ahmed, to an unknown location, according to Front Line and Maryam Al-Khawaja.
Al-Khawaja is a human rights leader who in February just quit as the director of the Middle East-North Africa region of Front Line, founded in Dublin, Ireland, in 2001 to protect human rights defenders at risk, Maryam Al-Khawaja said.
During Bahrain's recent protests, Al-Khawaja spread information about what it meant to be in civil disobedience, the daughter said.
This week, two other human rights groups accused the Bahraini government of "rampant arbitrary detentions" after security officers raided hospitals in a manhunt for wounded protesters.
Human Rights Watch demanded Friday that the Persian Gulf kingdom account for those who have been detained following anti-government protests and free anyone arrested arbitrarily.
"Bahrain has created a state of fear, not a state of safety," said Joe Stork, deputy Middle East director at Human Rights Watch.
Detainees have been beaten and abused, some told Human Rights Watch after being freed.
The group said at least 430 people had been detained since anti-government protests began on February 14, citing the opposition Wefaq party as the source of the number.
Human Rights Watch said it had been in touch with the families of a dozen missing people.
Meanwhile, Doctors Without Borders accused Bahraini forces of raiding medical facilities to crack down on protesters, prompting injured people to avoid going to hospitals.
"Health facilities are used as bait to identify and arrest those who dare seek treatment," said Latifa Ayada, the organization's medical coordinator. The group is also known by its French name, Medecins Sans Frontieres.
"Wounds, especially those inflicted by distinctive police and military gunfire, are used to identify people for arrest, and the denial of medical care is being used by Bahraini authorities to deter people from protesting," she said as Doctors Without Borders released a report into the phenomenon.
Human Rights Watch made similar accusations in the wake of the storming of Salmaniya Medical Complex on March 16.
The country's crown prince defended the government's actions in a speech Thursday.
"We were immensely concerned that some of our youth were pushed towards a destructive path and that the nation was drawn along with them," Prince Salman bin Hamad al-Khalifa said, according to an official transcript.
"We took necessary action to preserve lives and the livelihood and interests of all the people, based on our commitment to Islamic and Arab values," he said.
"The problem escalated beyond all limits. Freedoms were misused and overtaken by extremists and their agenda," he argued.
Protests swept the strategically important island kingdom earlier this year as populations across the Arab world rose up against their rulers.
Bahrain, where the U.S. Navy anchors its Fifth Fleet, is a small predominantly Shiite country governed by a Sunni royal family.
It called in Saudi Arabia and other regional troops to help end the protests last month.
CNN's Jenifer Fenton contributed to this report