(CNN) -- A fourth Emirati rights activist has been arrested in the United Arab Emirates, according to activist Mohammed al-Mansoori.

Abdullah al-Shehhi, who was part of a group of 133 Emirati nationals who petitioned the president on March 9 for direct elections, was taken from the Emirate of Ras Al Khaimah on Friday, al-Mansoori said.

Al-Shehhi previously served in the UAE armed forces and has been arrested three times before, al-Mansoori said. Three other activists have recently been arrested.

Ahmed Mansoor, an Emirati blogger who has called for reform in the UAE and who also signed the petition, was the first known activist to be detained.

Mansoor is being held in Al Wathba prison in Abu Dhabi, according to his wife Nadia. Mansoor has not been charged with a crime.

Dubai police have told Mansoor's attorney, Abdul Hamid Al Kumity, that two bottles of whiskey were found in Mansoor's house. Alcohol is available at hotels and select stores in the UAE, but Muslims are not allowed to buy or possess it.

Mansoor's wife acknowledged that there was alcohol in their house, but said they don't drink. The alcohol, in a small unopened box, was probably a gift from friends or family, she said.

Fahad Salem al-Shehhi, a friend of Mansoor's who helped him with his website, was detained April 9, according to al-Mansoori. He was taken from the Emirate of Ajman.

Nasser bin Ghaith, an Emirati writer who also maintains a website, was detained April 10, al-Mansoori said.

Officials in the UAE have not responded to persistent queries regarding the detentions.