COLOMBO, Sri Lanka (CNN) -- At least 50 people were detained during a house-to-house search following two bus bombings in Sri Lanka which killed at least 22 people Friday, police said.
Sri Lankan security officials inspect the bus that was the target of the roadside bomb attack.
One explosion on a crowded bus in Moratuwa, a southern suburb of Colombo, killed 21 commuters and wounded more than 53, police said.
A few hours later, a second blast hit a bus outside Sri Lanka's hill capital of Kandy killing one person, police said.
Police immediately accused Tamil Tiger rebels of carrying out both attacks.
The Moratuwa neighborhood where the first bomb exploded was sealed off as police and soldiers went house to house to search for suspects. They announced Saturday the detention of at least 50 people. 
Watch medics treat bus blast survivors »
Recently, there has been a marked increase in the number of bombings. Pro-rebel Web sites have accused Sri Lankan security forces of attacks on civilians in Wanni, the northern region dominated by them.
On Wednesday, a packed train heading to Colombo from the southern suburb of Panadura narrowly escaped severe damage when an explosion hit the track. The blast injured 23 commuters.
On May 26, an explosion on the same southern railway line killed nine and injured 84.
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