Leading Bahraini human rights activist Nabeel Rajab was arrested over his anti-regime twitter remarks.
Rajab, who heads the Bahrain Center for Human Rights (BCHR), had just returned to the country after an advocacy tour abroad.
He had served two years in prison for organizing anti-government protests before being released in May.
The Saudi-backed police questioned Rajab on Wednesday over his tweets.
“Legal measures have been taken to refer him to the general prosecution,” Manama said in a statement, adding that the activist had “insulted official bodies in his tweets.”
In one tweet shared on Sunday, Rajab said the Bahrainis that join the ISIL war in Syria and Iraq are actually members of security agencies belonging to the Persian Gulf monarchy.
“Many #Bahrain men who joined #terrorism & #ISIL came from security institutions and those institutions were the first ideological incubator,” Rajab wrote, using another abbreviation for the ISIL.
Rights group Human Rights First censured the arrest and called on the Al Khalifa regime to end “systematic harassment” of human rights activists.
Brian Dooley form Human Rights Watch also reacted to the detention, saying, “We are alarmed that the Bahraini government continues to target prominent human rights defenders in an effort to impede their vital work.”