* Interior Ministry takes firm line on marches
* Pockets of street unrest since Saturday's election
* Youth groups, opposition plan demonstration Saturday
By Sylvia Westall
KUWAIT, Dec 5 (Reuters) - Kuwait's Interior Ministry said it would take all necessary measures to prevent "unauthorised assembly" in the Gulf Arab state after dispersing protesters it said threw stones and tried to mow down police with cars.
Police have broken up a series of snap demonstrations outside the capital 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 last Saturday's parliamentary vote.
"A crowd marched in several residential areas in some districts in violation of laws and procedures," the Interior Ministry said in a statement carried by state news agency KUNA late on Tuesday, referring to a march the previous evening.
"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.
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 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 for years, but police broke up three big marches in October and November with tear gas, saying organisers did not have a permit.
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 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 government 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 Alaan news website showed pictures of injured protesters and said others had been detained. It said police used a water cannon to disperse crowds on Monday. Kuwaiti newspaper al-Rai said the protest was broken up with tear gas and stun grenades.
Kuwaitis protested again overnight on Tuesday in Sabah al-Nasser and Jahra, some of the more run-down neighbourhoods to the southwest of Kuwait City, al-Rai added.
On Wednesday, the daily published a photo of a police firing tear gas from a truck and a photo of a group of youths with headscarves wrapped around their faces throwing what it said were stones. It was not clear when the pictures taken.
Saturday's election was divisive due to the change to voting rules announced by emir Sheikh Sabah al-Ahmad al-Sabah six weeks before the poll. He said the changes fixed flaws in the voting system and would help ensure national unity and stability.
The opposition refused to contest the election, saying the new rule was designed to prevent it winning the majority it held in the last parliament and called for more demonstrations.