"The government cannot be responsible for the safety and security of civilians still living among LTTE [Liberation Tigers of Tamil Eelam] terrorists," it said.
Sri Lanka's military says it has designated a safe zone for civilians in a 32 sq km buffer zone on the A-35 main road which links Paranthan and Mullaitivu.
The government's designated safe zone is inside a gradually-shrinking rebel enclave north of the town of Mullaitivu.
But aid workers say that, in recent days, shells have fallen into the zone and people have been killed there. Both sides deny being responsible for firing into the area.
This whole issue of shelling at Puthukkudiyiruppu Hospital is based on false information
Lakshman Hulugalle Sri Lankan government spokesman
The Sri Lankan military said there had been more heavy fighting on Monday, with two rebel leaders critically wounded. There is no independent confirmation of the claim - journalists are not able to reach the front lines.
The army offensive has pushed the rebels into a 300 sq km (110 sq mile) corner of jungle in the north-east of the island, which aid agencies say also holds 250,000 civilians.
The government says the number of civilians is closer to 120,000 and that the army has a policy of not firing at civilians.
It accuses the Tamil Tigers of not allowing civilians to leave, saying they are being used as human shields.
The rebels say the civilians prefer to stay where they are under rebel "protection".
The government statement came a day after nine people were killed when shells hit a hospital in the area, according to the Red Cross.
There has been no word from the rebels on the government statement or on the shelling of the hospital, in the town of Puthukkudiyiruppu, in Mullaitivu district.
1976: Liberation Tigers of Tamil Eelam form in the north-east
1987: India deploys peace-keepers to Tamil areas but they leave in 1990
1993: President Premadasa killed by Tiger bomb
2001: Attack on airport destroys half Sri Lankan Airlines fleet
2002: Government and rebels agree ceasefire
2005: Mahinda Rajapaksa becomes president
2006: Heavy fighting resumes
2009: Army takes main rebel bases of Kilinochchi and Mullaitivu
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