Troops captured the strategic Elephant Pass last Friday
Heavy fighting is reported around the sole remaining Tamil Tiger stronghold of Mullaitivu in Sri Lanka as the army presses ahead with its offensive.
The defence ministry said troops had captured one "administration base" with jets bombing jungle hideouts.
Rebel sources have not commented on the claim, but say civilians have been wounded by artillery fire.
Meanwhile doctors in the recently captured town of Kilinochchi say that healthcare is breaking down.
The army says that it is pressing ahead after capturing Kilinochchi - the rebels' administrative centre - and the strategically important Elephant Pass.
Independent journalists are not allowed to report from the war zone so information regarding casualty figures cannot be verified.
A defence ministry statement on Tuesday said there were "bitter clashes" around Mullaitivu - the rebels' remaining major base.
It said an administration base, training camp and bunker line had been captured.
On Monday the military said it had attacked rebel positions from the air, including one base near Mullaitivu it said was known to be visited by rebel leader Velupillai Prabhakaran.
Since losing Elephant Pass, the main link to the Jaffna peninsula, last Friday, the rebels are operating in a region of jungle to the south of there and east of Kilinochchi.
The Tigers have not commented on the military situation but the pro-rebel TamilNet website said that many civilians had been wounded on Tuesday morning by artillery fire in the region.
Meanwhile, in a letter to the Sri Lankan government the Kilinochchi Medical Association (KMA) said that doctors and patients were now in a "pathetic situation" as gunfire continued to resound around the area.
The KMA said it was dealing with new civilian casualties every day and that ambulances could only be used infrequently. It said the situation was particularly difficult for pregnant mothers.
The KMA said it might have to stop operating in the area.
There has so far been no response from the government to the letter.
But the government said separately it was fully prepared to handle "the mass exodus of civilians" the fighting with the rebels might cause.
The Tigers have been fighting for a separate homeland for 25 years. At least 70,000 people have been killed in the insurgency.
The rebels had established a de facto state squeezed between government-controlled Jaffna in the north and the rest of the country.
But the latest military offensive has forced the rebels to give up much of their territory.