The report of fresh fighting came amid mounting international alarm over large-scale civilian deaths over the weekend due to shelling by the Sri Lankan army.
The United Nations has called for an immediate end to Sri Lanka's fighting after describing the weekend shelling of civilians as a "bloodbath" in which over 100 children were killed.
UN Secretary-General Ban Ki-moon urged the Colombo government "to explore all possible options to bring the conflict to an end without further bloodshed" and asked the separatist Tamil Tiger rebels to agree to a halt in the fighting.
"The secretary-general is appalled at the killing of hundreds of civilians in Sri Lanka over the weekend," his office said in a statement.
"Thousands of Sri Lankans have already died in the past several months due to the conflict, and more still remain in grave danger."
Artillery strikes on the small stretch of coastline still held by the Tamil Tiger guerrillas in the northeast of the island nation have caused major casualties among the tens of thousands of non-combatants, both sides reported.