Authorities in Bahrain have arrested four Shia Muslim activists on security related charges, officials say.
One of those held is Abd al-Jalil Singace, head of the Shia-dominated Haq Movement for Liberty and Democracy.
He was arrested on his return from London where he had been giving a lecture on human rights in Bahrain.
Correspondents say the arrests could heighten tensions between the Sunni-led government and Bahrain's Shia majority ahead of elections in October.
The Shia community has long complained of discrimination.
Three of the arrests were made on Sunday, while Mr Singace was detained on Saturday, the BNA state news agency reported, citing officials. BBC News