Kuwait City (AFP) - Human Rights Watch called on Kuwait on Monday to drop charges against former lawmaker Saleh al-Mulla, facing trial for tweets deemed critical of the emir and the Egyptian president.

"Kuwait authorities should also cease prosecutions against other peaceful critics," the New York-based rights group said in a statement.

Mulla, a liberal former lawmaker, was detained for five days before being released on bail on Sunday pending trial on February 15.

He was accused of insulting emir Sheikh Sabah al-Ahmad al-Sabah and Egyptian President Abdel Fattah al-Sisi, who visited the Gulf state last week. He was also charged with endangering Kuwaiti-Egyptian relations.

"Mulla's tweets are nothing more than political commentary,” said HRW's deputy Middle East and North Africa director, Nadim Houry. "If he is prosecuted for these tweets, it will be a textbook violation of protected free speech."

Since a political crisis in June 2012, Kuwaiti authorities have ramped up efforts to curtail dissent, with courts sentencing politicians, online activists and journalists to prison terms for exercising free speech rights, HRW said.

In 2014, the authorities used the constitution and a raft of restrictive laws to prosecute at least 13 people for criticising the government or institutions in blogs or on Twitter, Facebook or other social media, it added.

At least five of those prosecuted were convicted and sentenced to up to five years in prison.