MANAMA, Bahrain — A Bahraini appeals court on Thursday upheld a verdict against prominent rights activist Nabeel Rajab for insulting government ministries on Twitter, his lawyer said.

The decision confirms a January verdict against Rajab, who was sentenced to six months in prison for insulting the ministries of defense and interior in tweets alleging that Bahrain’s security institutions were incubators for extremist ideology.

Rajab had been allowed to remain free on bail pending appeal, but he was detained early last month on suspicion of separate charges related to different comments he made on Twitter. That case is still ongoing and he remains behind bars.

Rajab will seek to have the charges in Thursday’s decision overturned by the court of cassation, the last court of appeal, lawyer Jalila al-Sayed told The Associated Press.

Bahrain is an important Western ally in the Gulf, and hosts the U.S. Navy’s 5th Fleet.

The tiny island nation has faced four years of unrest led by its majority Shiites calling for greater political rights from the Sunni leadership. With help from security forces from neighboring Gulf states, Bahrain put down widespread protests in 2011. But occasional demonstrations still occur, and anti-government activists frequently clash with riot police.

Rajab is the president of the Bahrain Center for Human Rights and is active in other rights groups. He has been detained and prosecuted over Twitter comments in the past.

Amnesty International criticized Thursday’s decision, saying it shows a “complete disregard for the right to freedom of expression.” It called for Rajab to be released immediately and said his incarceration is proof that government promises of reform are “empty gestures.”

“Bahrain today remains a country where exercising freedom of speech is treated as a crime,” said Said Boumedouha, Amnesty’s deputy director for the Middle East.