Colombo - At least four civilians and 15 rebels were killed on Thursday in three related incidents in northern Sri Lanka as the military claimed they repulsed two rebel attacks and rebels fired artillery towards a populated town.

The clashes between rebels and security forces were reported in an islet in Jaffna, 390 kilometres north of the capital in the early hours of Thursday, the defence ministry said in a statement.

Initially the army and navy had repulsed a pre-dawn attack by rebels in the Chiraththivu islet killing 15 rebel after rebels had made a second attempt to reach the location by boat, the defence ministry said.

Three rebel boats were destroyed and the fourth was heavily damaged and sunk later, the defence ministry said, but did not give details of the casualties in the incident.

"Troops have also mounted heavy artillery attacks towards the fleeing terrorists (rebels) as enemy fatalities were expected to soar", the defence ministry said.

The defence statement claimed that later rebels had indiscriminately fired artillery towards the Jaffna town killing four civilians and injuring six others.

There was no independent confirmation about the incidents.

The Jaffna town and most parts of the Jaffna peninsula are controlled by the military.

Fighting in northern Sri Lanka has intensified during the past five months and more than 4,500 have been killed during the period. (dpa)