Twelve defence personnel were among 19 injured on Wednesday in an explosion on a bus in the central Sri Lankan town of Diyathalawa. Those injured included seven Armymen, five Air Force personnel and seven civilians, the military said.

The passenger bus was travelling from Jaffna to Diyathalawa, which has one of the main military training centres.

The military said they did not know the cause of the explosion yet, but suspected it could be a bomb or grenade, Reuters reported.

“The explosion cannot be ruled out as an act of terrorism as of yet,” military spokesperson Sumith Atapattu said, according to Daily Mirror. “Nevertheless, a highly explosive substance inside the bus may have caused the explosion.”

Atapattu said an investigation was under way. The police said the bus was heavily damaged, and the injured were taken to the Diyathalawa Hospital.

There have been no targeted attacks on the military in Sri Lanka since the three-decade civil war ended in 2009.