Two candidates from Prime Minister Ranil Wickremesinghe's party pulled out after a fellow candidate was gunned down by suspected Liberation Tigers of Tamil Eelam (LTTE) rebels in the district of Batticaloa on Monday, police said.

Wickremesinghe's party said it was seeking more protection for candidates.

It blamed the security breaches on President Chandrika Kumara-tunga, who took over the defence and interior ministry portfolios from the prime minister's control last November.

Independent monitors sought foreign help to reduce violence and vote-rigging and said they were particularly concerned about the embattled northern and eastern regions where the Tigers are active.

Four private election monitor organisations here jointly expressed concern over the murder of two political activists in the Batticaloa Monday and said they expected more trouble.

"We have the greatest concern about the condition of elections in the north and the east," spokesman Paikiasothy Saravanamuttu said, adding that they wanted more international observers deployed in those areas.

However, he said a heightened level of violence in the troubled regions could make it difficult to persuade foreigners to travel there to monitor the April 2 parliamentary election.

The vote is not being held in vast areas of the island's north-east where Tamil Tiger rebels are in control, but civilians from those areas are entitled to travel to neighbouring government-held villages and cast their ballots.

Tiger rebels are not contesting the polls, but have openly supported the moderate Tamil National Alliance, which is fielding Tiger proxies who could emerge as potential kingmakers.