Army troops and rebels exchanged fire in a pre-dawn clash across the de facto border that separates government- and rebel-held territories in Muhamalai on the northern Jaffna peninsula, leaving six guerrillas dead, a defense official said on condition of anonymity, citing government policy.
Hours later, soldiers confronted two guerrilla groups in northern Mannar district, killing eight insurgents, he said.
Also Thursday, a clash in Eastern Province's Palathoppur village resulted in the death of two rebels, the official said.
He said no government soldiers were killed in the battles.
Rebel spokesman Rasiah Ilanthirayan could not be reached for comment.
Both sides often release inflated casualty figures for the other side and lower their own.
The government has in recent months escalated military action against the region controlled by the guerrillas in the north after largely neutralizing the rebels in the east.
Later Thursday, a suicide jacket was found inside a passenger bus in Colombo, the Defense Ministry said.
The driver of the bus became suspicious of a bag and drove the vehicle to a police station, where police found a suicide jacket inside the bag, the ministry said.
Deputy Foreign Minister Hussain Bahila, meanwhile, said the government has banned the Tamils Rehabilitation Organization charity after investigations showed it was using donor funds to finance the rebels.
The charity is headquartered in the rebel-controlled town of Kilinochchi and has offices in 17 other countries. Last week, the United States froze the charity's assets there.
The Liberation Tigers of Tamil Eelam, as the rebels are officially known, have fought since 1983 to create an independent homeland for ethnic minority Tamils after a history of discrimination by governments controlled by majority Sinhalese.
More than 70,000 people have been killed in the conflict.
The rebels are among the early users of suicide bombing to attack political, economic and military targets. They have carried out more than 240 suicide bombings.