The Liberation Tigers of Tamil Eelam (LTTE) guerrillas fired at security forces in the district of Batticaloa, killing at least one soldier and wounding several others, military sources in the area said by telephone.
"There is heavy long-range fighting going on," a military official in Batticaloa said.
"Security forces are also retaliating."
The surge in attacks came hours after LTTE chief Velupillai Prabhakaran declared Monday that the movement had no option but to press for an independent state for the island's Tamil minority concentrated in the northern and eastern regions.
His declaration went back on a 2002 pledge to accept a federal solution under which the Tamils would enjoy broad autonomy.
That pledge opened the way for Norwegian-brokered political talks which collapsed in Geneva last month.
Prabhakaran said the Oslo-brokered truce had become "defunct" following military attacks against them, but stopped short of saying that his group was quitting the truce agreement.
He al