COLOMBO (AFP) -- Four Sri Lankan civilians have been killed in a roadside bomb attack allegedly carried out by government security forces, the Tamil Tiger rebels said Wednesday.

The Liberation Tigers of Tamil Eelam (LTTE) said the civilians were ambushed late Tuesday in Mannar district, where heavy fighting has been raging for weeks.
""Four displaced civilians from Mannar who were traveling in a tractor-trailer to their homes in Thadchanam aruthamadhu came under a claymore attack by the Sri Lanka army,"" the Tigers said.
""All four were killed instantly.""
The Tigers regularly accuse the Sri Lankan military of sending ""deep penetration units"" -- or small groups of commandos -- into the rebel-held north. Government defense officials refuse to discuss such operations.
The rebels usually follow their allegations of civilian casualties in their mini-state with retaliatory strikes elsewhere in the country.
Meanwhile, the Defense Ministry said two policemen were wounded in a roadside bomb attack in the north of the country Wednesday and blamed the Tiger rebels for the blast.
Since the beginning of the year, at least 1,823 rebels and 105 government soldiers have been killed in fighting, according to the Defense Ministry.
Aid workers say more than 170 civilians have also perished during the same period. The rebels have been fighting with the government's military for an independent homeland for minority Tamils since 1972.