Police found two powerful anti-personnel mines inside a passenger bus travelling from northern Sri Lanka on Monday.
Officials suspect that the explosives were being transported to the capital by Tamil Tiger rebels.
The bus was heading to Colombo from the northern town of Vavuniya on Sunday night when it was stopped at a road block in Anuradhapura district, 160 kilometers northeast of the capital, military spokesman Brig Prasad Samarasinghe said.
He said police found two strong anti-personnel mines, a hand grenade and two detonators inside a parcel on the bus.
All 45 passengers on the bus, the driver and the conductor were detained for questioning, he added.
Samarasinghe said the military believes that Tamil Tiger rebels may have been transporting the mines to Colombo.
The discovery comes as Sri Lanka's government and Tamil Tiger representatives prepare to meet in Geneva on Tuesday to save a four-year-old cease-fire that has come under threat because of frequent violence.
The government has accused the Tigers of increasingly using Claymore anti-personnel mines since December, killing 81 security forces personnel.
{{/usCountry}}The government has accused the Tigers of increasingly using Claymore anti-personnel mines since December, killing 81 security forces personnel.
{{/usCountry}}The rebels have denied the allegation and in turn accused the government of backing rival groups in a proxy war against the guerrillas.
Liberation Tigers of Tamil Eelam rebels began fighting the government in 1983 to create a separate state for minority Tamils accusing the majority Sinhalese-dominated state of discrimination.
About 65,000 people were killed in the conflict before the Norway-brokered ceasefire was signed on February 22, 2002.
Peace talks broke down in April 2003 when the rebels withdrew over disagreements on postwar power sharing.