KUWAIT'S lower court has sentenced an opposition youth activist to five years in jail "with immediate effect" for insulting the emir on Twitter, a rights group said.

"The court passed the maximum jail term against Mohammad Eid al-Ajmi for insulting the emir on Twitter," the director of the Kuwait Society for Human Rights, Mohammad al-Humaidi, said.

The ruling is not final as it will be appealed, but Ajmi will begin serving the sentence immediately, Mr Humaidi said.

Ajmi is the third opposition youth activist to be convicted for insulting the emir, Sheikh Sabah al-Ahmad al-Sabah, on Twitter. Last month the same court sentenced two tweeters to two years each in jail each on the same charge.

Ayyad al-Harbi and Rashed al-Enezi are both in prison as they await appeals court rulings on their cases.

Mr Humaidi said a large number of youth activists are on trial on similar charges, with verdicts expected in the coming weeks.

The criminal court is also scheduled to issue its verdict on Tuesday against three former opposition MPs for criticising the emir at a public rally on October 10.

Criticising the emir is illegal in Kuwait and is considered a state security charge. Those convicted of the offence face up to five years in jail.

US State Department spokeswoman Victoria Nuland said last month Washington had already raised with Kuwait its concern about such sentences.

The opposition has been staging regular demonstrations in protest at an amendment of the electoral law and the subsequent holding of a parliamentary election on December 1 on the basis of the amended legislation.

The opposition held a public rally late Saturday to express solidarity with Twitter users and former MPs on trial for expressing their opinion.

