Two buses were bombed within hours of each other Friday in Sri Lanka, officials said.
At least 21 people were killed and around 47 others wounded in the first attack, which occurred on a passenger bus during morning rush hour outside of the capital Colombo. At least two people were killed and 20 wounded in the second explosion, which went off in the hills of Kandy district, central Sri Lanka.
The country's military blamed the first attack on Tamil Tiger rebels, who did not immediately comment on the blast. If carried out by the rebels, the attack would show their ability to strike deep inside government territory despite a maze of security checkpoints around the capital and its suburbs.
Rebel spokesman Rasiah Ilanthirayan did not respond to calls seeking comment, but the rebels routinely deny such attacks.
The rebels, blamed for scores of suicide bombings and other attacks on civilians, are listed as a terrorist group by the United States, the European Union and India. Authorities have asked the public to remain vigilant in the wake of several bombings blamed on the rebels.
A blast blamed on rebels on a passenger train last month killed eight people and wounded 70 others near Colombo. Also last month, a bomb explosion deep in the rebel-held territory killed 16 people. Tamil Tigers blamed that blast on government forces — a charge the government denies.
The United Nations Office for the Coordination of Humanitarian Affairs says more than 200 civilians have died in bombings since the beginning of the year in both government-controlled ethnic majority Sinhalese areas and northern rebel-held territory.
The Tigers have fought since 1983 to create an independent homeland for ethnic minority Tamils, who have been marginalized by successive governments controlled by the majority Sinhalese. More than 70,000 people have been killed.
Fighting has escalated along the northern front lines since the government withdrew from a long-ignored cease-fire in January.
The government has pledged to capture the rebels' de facto state in the north and crush them by the end of the year. But diplomats and other observers say the army is facing more resistance than expected.