Colombo - Sri Lanka President Mahinda Rajapaksa Monday demanded that Tamil rebels release civilians "held hostage" in the country's war zones.

He alleged that civilians have been prevented from leaving rebel-held areas in the northern part of the country.

Some 300,000 civilians are living in rebel-controlled areas, where the Liberation Tigers of Tamil Eelam (LTTE) has kept people from leaving the zones, fearing a mass exodus would expose the rebels to major military offensives, officials claim.

Government troops in August 2006 launched an operation to liberate civilians in rebel-held areas in the north and east. The eastern province was retaken last year and parts of the north have come under government control.

Rebels are now confined to parts of two northern districts, Kilinochchi and Mullaitivu, 300 kilometres north of the capital.

Troops have stepped up ground, air and sea attacks on the rebels, but the presence of civilians has made operations difficult.

Tamil rebels claim that civilians have been killed in airstrikes.

The government has made a public appeal for minority Tamil civilians to leave the conflict zones and move to government-run shelter, but so far less than 1,000 have responded.

Some have taken the risk of defying the rebels and leaving while several others have taken risky journeys to reach army forward defence lines. (dpa)