A human rights activist in the United Arab Emirates (UAE) says three members of a religious society linked to the Muslim Brotherhood have been arrested.
The UAE has come down hard on the al-Islah society over the past year.
On 2 July, 68 people, most of them al-Islah members, were convicted of a plot to overthrow the government.
Human rights groups said the trial judge had failed to investigate "credible" allegations of torture of the defendants.
The new arrests have all occurred within the last week.
The latest is that of a senior communications engineer, Othman al-Shehhi.
The activist, who did not want to be named, says Mr Shehhi is being held in an unknown location, common practice in the UAE.
In another case, the family of a detained Qatari doctor have told the BBC that after nearly six months they still do not know where he is being held.
Dr Mahmoud al-Jaidah was detained at Dubai Airport on 26 February.
He is allowed one meeting a month with his family, after being driven blindfolded to a government building in Abu Dhabi.
"They [the authorities] play on his mood," Dr Jaidah's son, Hassan, says.
"They keep saying 'today you will be released' and they give him his clothes and he waits for hours but he is not released."
Hassan Jaidah says his father, who has yet to be charged, has no links to the Muslim Brotherhood.
"He is not associated with al-Islah or the Muslim Brothers at all. No-one who knows him can understand at all why he is being held."
The UAE government has said that all prisoners are treated according to the law and that any allegations of mistreatment are investigated.
Dr Jaidah, who works for Qatar Petroleum, finds himself caught between two countries with very different attitudes to the Muslim Brotherhood.
Qatar has long supported the Brotherhood, while the UAE view it as a serious threat.
Both countries are members of the Gulf Cooperation Council (GCC).
Dr Jaidah's case has parallels with that of Salah Yafai who was arrested at Dubai airport on 26 April 2013.
Mr Yafai, a fitness trainer and educator, is a member of the Bahrain al-Islah society.
The Bahraini citizen was held for almost seven weeks in an unknown location without charge. He was released on 15 June.
Earlier this week, the UAE government pardoned Norwegian Marte Deborah Dalelv, who was charged with a series of offences and sentenced to 16 months in prison after reporting being raped.
Her alleged attacker was also pardoned in a case which angered rights groups and the Norwegian authorities.