More than 60,000 people have been killed in the three-decade-old Tamil separatist conflict. The army's ground offensive was backed by Israeli-built Kfir jets which bombarded positions of the Liberation Tigers of Tamil Eelam (LTTE), the military said.
The LTTE accused Colombo of virtually declaring war on them with the latest offensive.
It vowed to resist an advance to open a canal which the LTTE blocked 10 days ago in an area under their control.
Defence officials said the military lost at least nine soldiers killed and 15 wounded but managed to take control of the sluice gates by Monday afternoon after heavy mortar bomb exchanges with the Tigers.
The defence ministry said "over 35" Tigers were killed, but there was no reaction from the guerrillas to the military claims.
Defence spokesman Keheliya Rambukwella said the "limited ground offensive" was a "humanitarian gesture" aimed at ending the LTTE blockade of the Maavilaru waterway in northeastern Trincomalee district that had deprived