Sri Lanka ? Suspected Tamil Tiger rebels blew up two passenger buses in Sri Lanka on today, killing 23 people and raising the specter of an escalating cycle of attacks on civilian targets.

An additional 67 people were wounded in the attacks, which came two days after a bombing that targeted civilians in Colombo, the capital. The government also blamed that blast on Tamil Tiger rebels, who have made such attacks a hallmark of their 25-year fight against Sri Lanka’s government.

“This could be the start of a worsening cycle of targeting civilians,” said Jehan Perera of National Peace Council, an independent activist group.

He said the attacks were likely “tit-for-tat kind of retaliation,” by the rebels, who accuse the military of killing ethnic minority Tamil civilians with mines and air raids.