* HRW says death toll in election violence at least 18
* Govt has denied use of presidential guard
* Election commission denies rigging accusation (Adds Lubumbashi security, detail on voting slips)
By Jonny Hogg
KINSHASA, Dec 2 (Reuters) - At least 18 people died in violence during the run-up to the Democratic Republic of Congo's elections this week, with most shot dead by soldiers from Joseph Kabila's presidential guard, U.S.-based Human Rights Watch said on Friday.
The figure, based on witness accounts and reports from local rights groups, is higher than most earlier estimates of the death count from unrest around the country before and during Monday's presidential and parliamentary votes.
The elections are seen as crucial to stabilising the vast central African country, but have been marred by organisational flaws, alleged fraud and clashes between rival political factions and the security forces.
The worst violence saw 14 people killed on Saturday, the final day of campaigning, when authorities cancelled political rallies and used force to clear opposition supporters from the streets of the capital, Kinshasa, HRW said in a statement.
The group said a presidential guard convoy opened fire on civilians, killing 12 and injuring dozens more including a pregnant woman. It added that the soldiers may have been retaliating after stones were thrown by opposition supporters.
"Elections don't give soldiers an excuse to randomly shoot at crowds. The authorities should immediately suspend those responsible for this unnecessary bloodshed and hold them to account," said senior HRW Africa researcher Anneke Van Woudenberg.
No one from the government was immediately available to comment on the HRW allegations on Friday. Security minister Adolphe Lumanu said on Wednesday the presidential guard had not been deployed during the violence in Kinshasa.
"It could have been people camouflaged or wearing presidential guard uniforms, (but) no element of the presidential guards was on the streets," he told Reuters.
Other incidents across the country included a hammer attack on an opposition politician at his home and the severe beating of an electoral observer after local people accused her of fraud, HRW said.
SECURITY TIGHTENED
In Lubumbashi, capital of the Katanga copper belt, military police were drafted in to protect vote compilation centres after an attack by suspected rebels on a polling station on Monday killed two policemen, the local government said.
With preliminary results from the presidential polls due next week, HRW joined the United Nations and others in calling for calm amid rumours and rising tensions, particularly in the largely pro-opposition capital.
"As the announcement of election results nears, it is crucial for all leaders to act responsibly and peacefully, win or lose," Van Woudenberg said.
Leading opposition candidate Etienne Tshisekedi has repeatedly said he will not accept defeat, while three other opposition candidates have called for the vote to be annulled, citing widespread fraud by the government.
The CENI national election commission denied opposition allegations that planes were still flying in from South Africa with ballot papers intended for use in rigging the vote.
One plane did bring 20 tonnes of extra ballot papers to Lubumbashi and Kinshasa on Tuesday to boost supplies in areas while voting was continuing, CENI spokesman Matthieu Mpita said.
"There was only one plane, we have no need to lie (about this)," he said. (Editing by Mark John and Andrew Heavens)
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