Bahrain's public prosecutor has detained and charged a man for a tweet saying he would boycott elections this month, with a rights group identifying him as a former lawmaker.
Opposition movements have been outlawed in Bahrain and hundreds of dissidents have been imprisoned - with many stripped of their nationality.
Ahead of legislative elections on November 24, Muhanna Al Shayji, the head of Bahrain's electoral crimes unit, said a man had been taken into custody over his Twitter account.
He has been charged with influencing public opinion and "obstructing the electoral process", Mr Al Shayji said in a statement released by the public prosecutor's office.
The London-based Bahrain Institute for Rights and Democracy identified the man as Ali Rashed Al Asheeri, a former member of parliament with the now-banned Al Wefaq opposition group.
Mr Al Asheeri on Thursday tweeted that he and his family would be boycotting the polls.
"I am a Bahraini citizen deprived of my civil and political rights. My family and I will therefore boycott the parliamentary and municipal elections. No to the laws of political isolation," he wrote.
Bahraini authorities have banned the country's two main opposition groups - the Shiite Al Wefaq and secular Waad - from submitting candidates for parliament.
The Sunni-ruled Gulf kingdom has been hit by waves of unrest since 2011, when security forces crushed Shiite-led protests demanding a constitutional monarchy and an elected prime minister.
Bahraini authorities accuses Shiite Iran of provoking unrest in the kingdom, an allegation Tehran denies.
Sheikh Ali Salman, who headed the Al Wefaq group, was sentenced to life in prison on November 4 for spying for rival Gulf state Qatar, in a ruling rights groups have called a travesty.
Human rights groups have frequently said cases against activists in Bahrain - men and women, religious and secular - fail to meet the basic standards of fair trials.
Amnesty International and Human Rights Watch categorise many of those jailed as prisoners of conscience.
Bahrain, a key ally of the United States, is home to the US Fifth Fleet and a permanent British military base.
US President Donald Trump has eased restrictions on arms sales to Bahrain since taking office, which had been tightened over the kingdom's treatment of protesters.