DUBAI — In the early hours of Tuesday morning, Mohamed al-Roken drove toward his local police station here to report that his son and son-in-law were missing. Along the way, he found himself surrounded by plainclothes security officers and detained, according to his family.
Mr. Roken, along with his son, Rashid, and son-in-law, Abdulla al-Hajeri, are 3 of at least 14 Emiratis who have been arrested since Monday morning by the United Arab Emirates state security apparatus, human rights advocates and family members said. Nearly two dozen activists are now being held by the authorities.
The arrests are part of a widening crackdown on U.A.E. citizens, some of them Islamists but also academics and stateless people known as bidoon.
“This may be a way to frighten opposition on all sides,” said Christopher Davidson, an expert on Gulf issues at Durham University in England.
This week’s crackdown comes days before the expected start of the Islamic holy month of Ramadan and highlights an increasingly public conflict in the Emirates.
Unlike many Arab countries, the Emirates have emerged largely unscathed from the unrest that has spread across the region from the Arab Spring that began 18 months ago.
But a debate on free speech and political freedom among Emiratis has emerged, as the leaders here try to maintain a balance between the more conservative character of their neighbors and a desire to preserve their status as a Western-style business hub.
While the trend among natives is still to keep quiet and enjoy the comfortable life provided by the rulers, a small group of activists is agitating for greater political participation — and drawing the attention of the authorities.
Bushra al-Roken, Mohamed al-Roken’s daughter, said the family received a phone call from her father at 1:30 a.m. on Tuesday.
“We couldn’t understand that much,” she said, “but we could hear voices and my father saying, ‘They’re taking me.”’
On Sunday, the state media issued a statement saying the authorities were investigating “a group of people who established and ran an organization which aims to commit crimes against the security and constitution of the country.” Members of this group have “connections with foreign organizations and agendas,” the statement added.
Mr. Roken, a lawyer, was defending several Emiratis who had been arrested on charges of threatening state security. Many of those arrested are members of Al Islah Reform and Social Guidance Association, which holds beliefs similar to those of the Muslim Brotherhood, the mainstream Islamic organization.
Many of these activists say they would like to see Islam play a more prominent role in everyday life in the Emirates, and they have also called for a more democratic political system in the country, a group of seven principalities ruled by hereditary emirs.
The authorities regard Al Islah as a homegrown proxy for the Muslim Brotherhood, a group that they see as gaining influence in the region — especially after the recent election of a Brotherhood candidate, Mohamed Morsi, as Egypt’s president.
The families of those detained are scrambling to find them. Asma al-Siddiq said her husband, Omran al-Redhwan, was arrested Monday morning at the Abu Dhabi Islamic Bank in Sharjah, where he works as a legal consultant. Ms. Siddiq said she had not heard from the authorities about the reason for her husband’s arrest or where he was being held.
“I am looking at social media sites, Twitter to try to find information,” she said.
The arrests followed the deportation to Thailand on Monday morning of Ahmed Abdul Khaleq, a resident of Ajman, the smallest of the emirates, who was one of the original activists arrested and tried last year.
The men, who were convicted in November of threatening state security and insulting the country’s leaders, were sentenced to three years in prison before being pardoned days after the verdict.
Mr. Khaleq was born in the Emirates, but he is a bidoon, or stateless Arab.
Estimates of the number of bidoon range from 10,000 to 100,000, human-rights advocates say. They belong to families with ties to other parts of the Gulf or Iran, or that failed to obtain citizenship when the United Arab Emirates was formed in 1971. They say they are cut out of the Emirates’ generous social welfare system and complain of discrimination in jobs.
Last month, Mr. Khaleq was given a choice of where to be deported — Bangladesh, India, Iran, Pakistan or Thailand. He chose Thailand, though he had no relations there, said Ahmed Mansoor, a human rights activist and blogger who was among the group arrested with Mr. Abdul Khaleq last year.