A controversial Tunisian pro-Islamist militia said on Sunday police had released two of its officials arrested at a prohibited meeting.
On Saturday, police detained Imed Deghij and Mohamed Amine Agrebi, officials from the League for the Protection of the Revolution, and a handful of their supporters for several hours.
The militia, which the opposition says has ties to the ruling Islamist Ennahda party, denounced the arrests and called for demonstrations in Tunis on June 1.
"It is impossible to bring Tunisia back to dictatorship... back to repression and corruption," the LPR said on its Facebook page.
It said the protest, set for the centre of Tunis, was "to tell all the political parties that if they are there, it is thanks to us".
The League was formed, with the support of Ennahda and allies of President Moncef Marzouki, as safeguard of the country's January 2011 revolution.
For months the opposition has demanded the disbanding of LPR, accusing it of using violence to intimidate its critics, but Ennahda has steadfastly refused to disband it.
In December, members of the LPR tok part in an attack on a hotel in Djerba in the south where a meeting of the opposition Nidaa Tounes was being held.
League members were accused of lynching a Nidaa Tounes activist in autumn last year and also of attacking the headquarters of the UGTT, the country's largest trade union, in December.