KUWAIT, April 12 (Reuters) - Kuwaiti lawmakers voted in favour of a legal amendment on Thursday which could make insulting God and the Prophet Mohammad punishable by death, after a case of suspected blasphemy on Twitter caused an uproar in the Gulf Arab state.

Members of Parliament must vote on the proposal again in a second session and it would need the approval of the country's ruler before becoming law.

The amendment was backed by 46 votes, while four opposed it and others abstained. Those in favour included all 15 members of the cabinet.

Blasphemy is illegal in Kuwait under a 1961 publications law and at present carries a jail term, the length of which depends on the severity of the comments and their perceived effect on society, lawyers say.

Islamist MPs proposed toughening the law last month after authorities arrested a Kuwaiti man they said had defamed the Prophet, his companions and his wife on the Twitter messaging site.

The man, identified by his lawyer as Hamad al-Naqi, has told police his account was hacked and he did not post the comments. He is now in pre-trial detention.

Dozens of Sunni activists protested to condemn Naqi, who is from Kuwait's Shi'ite Muslim minority. Some members of parliament have called for him to be executed.

Shi'ite parliamentarians voted against the amendment on Thursday.

Several of Kuwait's main newspapers have run editorials condemning Naqi, while others have accused Sunni activists of over-reacting.

Kuwaiti MPs from across the political spectrum have voiced concern about sectarian tension. Shi'ites make up about 30 percent of Kuwait's 1 million native citizens.

Naqi's lawyer, Khaled al-Shatti, told Reuters on April 3 that if his client was found guilty of insulting the Prophet the penalty would be one year in jail. If he was also convicted of "sedition" - specifically inciting strife - the penalty would be a maximum of 10 years in jail.

Twitter is popular in Kuwait, where many politicians, journalists and other public figures use the micro-blogging site to debate current affairs and share gossip. (Reporting by Mahmoud Harbi, Writing by Sylvia Westall; Editing by Sami Aboudi and Janet Lawrence)