* Interior Ministry takes firm line on marches
* Pockets of street unrest since Saturday's election
* Youth groups, opposition plan demonstration Saturday
KUWAIT, Dec 5 (Reuters) - Hundreds of young Kuwaitis chanting protest slogans gathered at a roundabout outside the Gulf Arab state's capital on Wednesday in the latest snap demonstration since a parliamentary election on Saturday.
Police have broken up several marches outside Kuwait City since Saturday, part of protests triggered by changes to voting rules the opposition said were designed to skew elections in favour of pro-government candidates.
The opposition, which includes Islamist and populist politicians, refused to stand in the election in protest at a decree issued by Kuwait's ruler which reduced the number of votes per citizens to one from four.
The young men protesting on Wednesday, wearing surgical masks, balaclavas and scarves wrapped around their faces, marched along a main street in a district southwest of the capital and were followed by scores of cars honking their horns.
The men let off fireworks and chanted "One, one, one, we don't want one vote!"
Small groups of police gathered in the surrounding streets.
Tens of thousands marched peacefully in the capital on Friday in what organisers said was the largest protest in Kuwaiti history, to urge people to shun the election.
The authorised march, attended by men, women and children, was organised by youth groups and backed by opposition politicians on the eve of the election. They plan another march on Saturday.
Rallies outside parliament have been held regularly and peacefully in the major oil producer for years, but police broke up three big marches in October and November with tear gas, saying organisers did not have a permit.
BAN ON UNLICENSED GATHERINGS
Protesters in those marches said they were pushing for reform, not an Arab Spring-style revolution like those that have ousted four Arab autocratic rulers since early last year.
Kuwait, a U.S. ally and OPEC member, allows more political freedom than other Gulf Arab states but has been more readily reinforcing a ban on public gatherings of more than 20 people without a permit.
The Interior Ministry said late on Tuesday it would take all necessary measures to prevent "unauthorised assembly" after dispersing protesters it said threw stones and tried to mow down police with cars.
"The Interior Ministry will never allow any unauthorised gatherings whatever their aims and needs are." It said several police were hurt on Monday when some protesters in cars attempted to run over police. Others were hit by stones.
The government had made it clear last month it would suppress unauthorised street protests to protect public safety, but analysts say the hard line could provoke deeper unrest.
The ruling emir, Sheikh Sabah al-Ahmad al-Sabah, announced the change to the voting rules six weeks before the poll. He said it would fix flaws in the voting system and would help ensure national unity and stability.
The opposition said the new rule was designed to prevent it winning the majority it held in the last parliament and has called for more demonstrations.