(Adds U.S. comment, paragraphs 10-11)
KUWAIT, Feb 5 (Reuters) - A Kuwaiti court sentenced three former opposition lawmakers to three years in jail on Tuesday for comments deemed offensive toward the ruling emir, the second such conviction in three days.
The three ex-lawmakers - Islamists Falah al-Sawwagh and Bader al-Dahum, and populist Khaled al-Tahus - were arrested in October after an opposition-led protest where riot police used teargas and stun grenades.
Tens of thousands joined similar protests in October over changes to an electoral law passed by the emir, who is described as "immune and inviolable" in the constitution.
The emir said the old voting system was flawed and that his changes were necessary for security and stability. Opposition MPs said the changes, made six weeks before the election, would limit their prospects and boycotted the vote.
The court case focused on comments about Sheikh Sabah al-Ahmad al-Sabah made before the rally at a diwaniya, a traditional evening social gathering, the news site alaan.cc reported. An official at the court in Kuwait City confirmed the verdict and said the men could appeal the ruling.
The U.S. ally and major oil exporter has been taking a firmer line on politically sensitive comments in recent months. On Sunday it sentenced a political activist to five years in prison for insulting the emir on Twitter.
The government said afterwards that it supported free speech but must act against illegal comments about the emir.
Kuwait allows more dissent than other Gulf states and has avoided the kind of mass unrest that unseated four heads of Arab states in 2011. The electoral changes, however, triggered some of the biggest protest marches in Kuwait's history.
In Washington, the U.S. State Department urged Kuwait to permit greater freedom of expression.
"We ... oppose laws that curb the peaceful exercise of free expression," State Department spokeswoman Victoria Nuland told reporters, reiterating a previous call for Kuwait "to adhere to its own tradition of respect for freedom of expression."
Amnesty International said in November that Kuwait had increased restrictions on freedom of expression and assembly, and urged it to protect users of social media, whether they supported or opposed the government.
In a statement reacting to Tuesday's court ruling, the Ministry of Information said all citizens were guaranteed a fair trial and that the judicial system was transparent.
"All citizens, regardless of their position, are equal in the eyes of the law," it said. (Reporting by Sylvia Westall; Editing by Sami Aboudi, Kevin Liffey and Philip Barbara)