Tamil Tiger rebels are putting up stiff resistance as government troops close on their political capital in Sri Lanka's war-torn north, the defence ministry said on Monday.

Troops captured two bunkers and destroyed another on the western defences of of Kilinochchi on Sunday as the offensive continued in heavy rain, the ministry said.

"Terrorists have also put on stiff resistance in the area despite sustaining heavy losses," it said in a statement.

On Sunday, the ministry said troops were within "kissing distance" of Kilinochchi, the political headquarters of the Liberation Tigers of Tamil Eelam (LTTE).

The government has been saying that the fall of Kilinochchi was imminent since September, but intense rebel resistance and monsoon rains have slowed the military push.

The ministry did not give details of its casualties, while there was no comment from the guerrillas. There were no independent accounts of the fighting.

The LTTE has admitted losing ground to government troops but their leader, Velupillai Prabhakaran, vowed in his annual speech last month to fight on.

The guerrillas, who began their struggle for a separate Tamil homeland in 1972, are facing the Sri Lankan army's biggest ever offensive.