KUWAIT (Reuters) - Kuwaiti authorities must allow protesters to gather peacefully and express their views without the threat of arrest, Amnesty International said ahead of an opposition march over voting rules planned later this week.

Protesters plan a march in central Kuwait on Friday, on the eve of parliamentary elections which the opposition is boycotting in protest.

Opposition politicians and youth protest groups say new voting rules introduced by Kuwait's 83-year-old ruler by decree in October are an attempt to skew the December 1 election in favour of pro-government candidates.

The emir, Sheikh Sabah al-Ahmad al-Sabah, says the voting system is flawed and that the changes are constitutional and needed for the sake of Kuwait's "security and stability".

"Protesters must be allowed to peacefully assemble to voice their views without hindrance or fear of arrest and such gatherings should be permitted to form into marches or other types of peaceful protest," London-based Amnesty said in a statement posted on its website.

Kuwait's prime minister said on Monday that the planned protest march had been given permission to go ahead, in a step which could ease tensions ahead of the vote.

Kuwait allows the most dissent among the Gulf Arab states and its citizens often hold rallies in a designated area outside parliament. But recent protest marches in the streets beyond have been broken up by police using tear gas, smoke bombs and baton charges.

Authorities are keen to prevent the kind of unrest Kuwait experienced on October 21, when thousands of demonstrators tried to reach government headquarters in the largest march and were forcibly dispersed by police.

"The right to protest and freedom of speech are enshrined in Kuwait's constitution," Information Ministry official Tareq al-Mezrem said in response to the Amnesty statement.

ADVANCE NOTICE OF PROTESTS

He said advance notice of large marches needed to be given and that protesters had followed this process correctly for the sanctioned November 30 rally.

"While the government respects the rights of citizens to raise their voices, we call upon them to respect the law and protest peacefully," he added.

The new voting system is aimed at ensuring fair representation in parliament and bringing Kuwait "in line with other democracies," he said.

Kuwait has the most open political system in the Gulf Arab region with an elected parliament that has legislative powers and the power to question ministers. The emir has the final say in state matters, selects the prime minister who in turn picks a cabinet, with the top posts held by ruling family members.

Amnesty said users of social media should also be able to enjoy protection whether they support or oppose the government, as long as they did not incite racial hatred or violence.

Sheikh Sabah is on a state visit to Britain this week and Amnesty called on Prime Minister David Cameron to tell the emir that Kuwait "needs to avoid a crackdown."

"The Kuwaiti authorities need to call a halt to increasing restrictions on freedom of expression and assembly."

Several people, including politicians, have been arrested for remarks deemed to undermine the status of the emir.

The most prominent was Musallam al-Barrak, a former parliamentarian who polled strongly in the last elections in February. He made remarks about the emir at a public rally.

Earlier this month four Kuwaitis were arrested for making remarks about the emir on Twitter that were also deemed illegal.

Amnesty reiterated a call on Kuwait to drop the charges against Barrak, as well as others held either for making remarks about the emir or for taking part in demonstrations.

(Reporting by Sylvia Westall; Editing by Mark Heinrich)