DUBAI - Bahrain on Wednesday charged 60 people with forming a "terrorist group", with a judicial source saying all 60 are Shias, as authorities tighten their grip on dissent in the kingdom.

The 60 face a mass trial, scheduled to open on August 22, for charges including "forming a terrorist group, training in the use of weapons and explosives with the aim of carrying out terrorist attacks and the deliberate killing of policemen", public prosecutor Ahmad al-Hamadi said. Thirteen of the defendants have "fled to Iran, Iraq and Germany" and will be tried in absentia, state news agency BNA reported.

Speaking on condition of anonymity, a judicial source told AFP that all 60 of those charged were Shias.

Authorities have jailed hundreds of people since 2011 in connection with Shia-led protests demanding an elected government in a country ruled for 200 years by the Al-Khalifa dynasty.

Several high-profile clerics and activists, including Sunnis, have been jailed and stripped of citizenship on charges including slander against the state.

The government accuses neighbouring Tehran of provoking dissent in the tiny kingdom, located in the Gulf between Saudi Arabia, Qatar and Iran. Bahrain, an ally of the United States and home to its Fifth Fleet, has drawn harsh criticism from international human rights groups for its crackdown on protesters.