The Liberation Tigers of Tamil Eelam (LTTE) launched a pre-dawn assault against five key military camps in the coastal Batticaloa district and several civilians were caught in the crossfire, local military officials said.
They said about 40 civilians were wounded in rebel mortar bomb attacks that also hit a relief centre.The security forces recovered the bodies of 10 rebels, including a woman fighter, killed in the pre-dawn battle, they said.
The military said four soldiers were killed and 30 wounded. In another confrontation in the island's north, five Tigers were killed, the military said.
In the east of the island, at least 300 Tiger fighters were involved in simultaneous attacks against the military camps, the defence ministry said.
The air force deployed Israeli-built Kfir jets to bomb two positions in the Batticaloa district, Ajantha Silva, an air force spokesman, said.
The LTTE said their attack on the camps was pre-emptive, but said they had no firm details on casualties.
"Our troops launched a pre-emptive strike on the Sri Lankan military build-up, the purpose of which is to launch operations into our administered area," Rasiah Ilanthiraiyan, Tiger military spokesman, said from the rebels' de facto capital of Kilinochchi.
"They also want to disrupt the harvest and to make more IDPs (internally displaced people)," he added. "With our pre-emptive strike, we were able to stop the havoc...I accept there is a possibility of casualties on our side."
The conflict in Sri Lanka has killed more than 60,000 people since the Tamil Tiger rebels began their armed campaign for a separate homeland in 1982.
About 4,000 people have been killed in a new wave of fighting since December 2005. The fighting comes despite a truce in place since February 2002.