Bahraini police on Wednesday detained prominent rights activist Nabil Rajab after questioning him over remarks posted on Twitter deemed offensive to the security forces, the interior ministry said.
Rajab acknowledged during questioning that he was responsible for the remarks posted on his Twitter account, and "legal measures have been taken to refer him to the general prosecution", a ministry statement said.
It said Rajab "insulted official bodies in his tweets".
In one tweet posted on Sunday, Rajab charged that Bahrainis allegedly joining Islamist extremists in Syria were originally members of the Sunni-ruled kingdom's security forces.
"Many #Bahrain men who joined #terrorism & #ISIS came from security institutions and those institutions were the first ideological incubator," he wrote, referring to one acronym for the Islamic State jihadist group.
Rajab, who heads the Bahrain Centre for Human Rights, was released in May after serving two years in jail for participating in unauthorised protests.
The vocal activist had led anti-government protests following a crackdown on Shiite-led demonstrations against the Al-Khalifa ruling family in March 2011.
Bahrain continues to witness sporadic protests which often spiral into clashes with police.