Mahinda Rajapakse, Sri Lanka's president, called for the Tamil Tigers to surrender after government troops retook the town of Pooneryn after 15 years under the separatists' control.
The defence ministry said on Saturday that government forces now controlled the entire western coast of the Indian Ocean island.
There was no immediate comment from the Tamil Tigers, but the movement has previously conceded that many of their fighters had pulled back into territory in the north of the country since the middle of last year.
The Tamil Tigers had used the coastal area to launch artillery strikes against a military airbase on the northern edge of the government-controlled Jaffna peninsula.
The military claims that the LTTE smuggles arms, explosives and other supplies from the Indian state of Tamil Nadu, which is separated from Sri Lanka's northwestern coast by the narrow Palk Strait.
In recent months, government-backed forces stepped up their offensive in a bid to capture the town of Kilinochchi, the LTTE's de facto capital, but bad weather and Tamil Tiger resistance has slowed those operations.
"Capturing Pooneryn is very significant, but now they have a more responsible task of securing the areas captured," Iqbal Athas, a Colombo-based defence analyst, said.
"The rebels are throwing all they have to secure Kilinochchi."
The LTTE has been fighting since 1972 to carve out a homeland for minority Tamils in the predominantly Sinhalese country.
Tens of thousands of people have been killed in the conflict.
The military has stopped releasing its own casualties figures in daily bulletins since last month, but official figures tabled in parliament show that 1,269 troops had died in the first 10 months of this year.
The military claims it has killed more than 7,500 LTTE fighters since they pulled out of a Norwegian-brokered truce in January.
It is impossible to independently confirm casualty figures or details of military operations in the north of the island as the area is closed to journalists and the two sides often give differing accounts.