A prominent human rights activist detained for posting tweets deemed “insulting” to Bahrain’s Ministy of Interior must be released, Amnesty International said.Nabeel Rajab, the director of the Bahrain Centre for Human Rights, was arrested on Saturday evening and has been charged with “insulting a national institution”.”This is the Bahraini authorities’ latest attempt to clamp down on dissenting voices in the country,” said Philip Luther, Director of Amnesty International’s Middle East and North Africa Programme.”Nabeel Rajab is a prisoner of conscience and he must be immediately and unconditionally released.”Rajab was arrested on arrival at Bahrain International Airport, following a trip to Denmark, Sweden and finally Lebanon. Just before travelling abroad, he had been summoned for questioning by the Public Prosecutor after the Ministry of Interior accused him of sending “insulting” tweets. He did not attend because of his travel. The activist was brought to the Public Prosecutor’s Office on Sunday and interrogated. Rajab’s lawyer said about eight insulting tweets were mentioned, and he was given a seven-day detention order pending investigation. Rajab also appeared before a lower criminal court on Sunday in another case against him, in which he is charged with calling for participation in illegal gatherings in which some protesters acted violently. The trial was adjourned until 22 May.”Nabeel Rajab has not called for the use of violence – in fact he has publically stated he is against the use of violence in protests – so the authorities have no grounds to punish him,” said Philip Luther.”Peaceful public gatherings and freedom of expression must be allowed in Bahrain, in line with the country’s international obligations to uphold these rights.”Rajab has denied all charges against him and is currently held in al-Houra police station in Manama.Repression of government critics has continued in Bahrain despite government pledges to implement reforms recommended in November, when a team of international jurists published a key report on the crackdown on protests. The Bahrain Independent Commission of Inquiry – chaired by Egyptian jurist Cherif Bassiouni – prescribed wide-ranging change that included decriminalizing public gatherings. However, key recommendations have so far not been implemented. Bahrain’s High Criminal Court of Appeal today held its first session in the case of 21 prominent opposition activists, seven of whom were being tried in absentia. However, the trial was adjourned until 21 May because two defendants are in hospital. One of the men, human rights activist Abdulhadi Al-Khawaja, has been on hunger strike for more than two months in protest at his unfair imprisonment. Amnesty International understands his physical condition is critical. Amnesty International considers all those currently detained in the case as prisoners of conscience and is calling for their immediate and unconditional release.