A Bahraini human rights activist has been sentenced to five years in prison for criticising Saudi Arabia’s air strikes in Yemen and accusing Bahrain’s prison authorities of torture, his lawyer and fellow activists said.

The US, which has a major naval base in Bahrain, has expressed concern about the case of Nabeel Rajab, a leading figure in pro-democracy protests that swept Bahrain in 2011 who was already serving a two-year sentence over a news interview in which he said Bahrain tortured political prisoners.

The new convictions were for “insulting a neighbouring country” and “insulting national institutions” in comments posted on Twitter, activists said.

There was no immediate comment from the Bahraini government.

Sayed Ahmed Alwadaei, an activist with the London-based Bahrain Institute for Rights and Democracy (BIRD), said Bahraini courts were barring citizens from criticising the authorities.

“Instead of rewarding Nabeel Rajab for his brave and commendable exposure of human rights abuses and advocacy for peace, the authorities have chosen to punish the messenger,” he said.

Bahrain has cracked down on perceived threats since protests in 2011 inspired by the Arab springand led mainly by members of its majority Shia population were quashed with help from Gulf Arab neighbours.

The Sunni-led monarchy has closed two main political groups, revoked the citizenship of a top Shia cleric, banned activists from travelling and put some on trial.

Authorities accuse Iran, the region’s majority Shia power, of being behind years of militant bomb and gun attacks on its security forces, something Iran denies.

Bahrain hosts the US fifth fleet, a a major naval base in a region where tensions between Bahrain’s main ally, Saudi Arabia, and Iran are on the rise.

A US embassy representative attended an earlier hearing for Rajab, the state department spokeswoman Heather Nauert said on Tuesday, adding that Washington was disappointed his earlier verdict had been upheld.

“He’s a prominent human rights activist ... we continue to have conversations with the government of Bahrain about our very serious concerns about this,” she said.

Rajab’s son Adam tweeted on Wednesday that his father laughed and flashed a peace sign in court when the verdict was delivered.