The move follows reports that the separatist Tamil Tigers may have acquired light aircraft that could be used for aerial attacks.

Military officials say that they have no firm evidence of the rebels' flying capability but admit that the Sri Lankan navy had opened fire at unidentified flying objects in the north of the country last week.

Heightened security for Velupillai Prabhakaran's birthday

The Sri Lankan parliament building, located on a lake island near the capital, is already closely guarded.

Visitors to the parliament are thoroughly searched and there is a ban on vehicles entering the complex.

Tamil Tigers have made a number of spectacular suicide bomb attacks in the capital and elsewhere during their 15-year campaign for an independent homeland.

Tiger remembrance week

Security has been tightened throughout Sri Lanka as the Tigers mark a week of remembrance of their members killed in the fighting.

The week coincides with the birthday of their leader, Velupillai Prabhakaran.

In previous years the period leading up to and including his birthday, known as Heroes Week to the Tigers, has seen a number of violent attacks.

The number of checkpoints in Colombo and other major towns has been increased, and troops have been told to take extra precautions.

There have been reports of increased activity in the Tiger-held areas, but the rebels say this is a time to commemorate those who have died.