COLOMBO, Sri Lanka (CNN) -- Sri Lanka's military said on Tuesday it shot down a plane used by the Tamil Tiger rebels.

The single-engine, four-seater plane was gunned down as the rebels attacked a military base in Vavuniya, the northernmost town under government control, an Air Force official said.

The attack on the base occurred at about 3:20 a.m. (5:50 p.m. ET Monday), killing six soldiers, the official said.

The number of casualties from the plane was not immediately known.

A spokesman for the rebel group could not be reached to confirm that the plane was downed and it could not be independently verified.

In the past, both sides have exaggerated accounts of military operations.

The rebels carried out their first airstrike in March 2007, using a small propeller plane to bomb an air force base outside the capital, Colombo, The Associated Press reported.

Also on Tuesday, the government asked United Nations agencies and non-governmental organizations to leave parts of the northern Wanni region; security sources told CNN the order was a prelude to a government bombing campaign of rebel positions there.

The fighting in Sri Lanka pits government forces in a country dominated by the Sinhalese ethnic group against rebels from the Tamil minority.

The rebels, formally known as the Liberation Tigers of Tamil Eelam (LTTE), are fighting for the creation of an independent nation, citing discrimination by the Sinhalese.

The rebels have been fighting for an independent state in the north and east since 1983, following decades of marginalization of ethnic Tamils by governments dominated by the Sinhalese majority.

More than 70,000 people have been killed in the conflict, according to AP reports.