DUBAI: A Bahrain court on Tuesday postponed the trial of Shiite opposition leader Nabil Rajab, a judicial source said, as authorities take increasingly harsh measures against dissent in the Gulf kingdom.

Rajab, who was present at Tuesday's hearing, is charged with spreading "rumors and false news" via televised interviews in 2014 and 2015 in which he criticised authorities.

The next hearing in Rajab's case is scheduled for April 16. The presiding judge also denied his lawyer's request for release on bail, the judicial source said.

Tuesday was the fourth suspension in Rajab's trial, which opened in January.

The high-profile activist, a founder of the non-governmental Bahrain Center for Human Rights, also faces a separate trial for a series of tweets deemed insulting to Saudi Arabia which has also been postponed multiple times.

The next hearing in that case is scheduled for March 22.

Rights groups including Amnesty International have called for authorities to release Rajab on the grounds that he is a prisoner of conscience.

Sunni-ruled Bahrain has been rocked by sporadic unrest since 2011, when a wave of popular protests demanding an elected government erupted in the majority-Shiite kingdom.

Authorities have cracked down on political dissent since then, and many leading political activists are in exile or behind bars. Access to foreign journalists is also largely off-limits.

Home to the US Navy's Fifth Fleet, Bahrain has noticeably tightened its grip on political dissent in recent weeks.

The upper house of parliament, appointed by the king, on Sunday voted unanimously to allow military courts to try civilians arrested in connection with terrorism, a vague legal term.

Bahrain has also moved to outlaw political opposition parties.

The justice ministry on Monday filed a lawsuit to dissolve the National Democratic Action Society (Waad), the country's main secular opposition party.

Al-Wefaq, Bahrain's main Shiite opposition group, was dissolved by court order in late 2016.