COLOMBO (Reuters) - A grenade exploded on a bus in Sri Lanka on Wednesday, injuring 19 people, including 12 military personnel, the prime minister said, but the military ruled out the possibility that the incident was an attack.

Since the end of Sri Lanka’s nearly three-decade civil war in 2009 there have been no targeted attacks on the military.

“It has been revealed from the initial investigations that it was a grenade in a bag of a passenger which exploded,” Prime Minister Ranil Wickremesinghe told parliament

“Further investigations are going on.”

He gave no details about the identity of the passenger nor did he say if the blast was accidental.

But the military spokesman, Sumith Atapattu, said the blast was not the result of an attack.

“We rule out any terrorist attack. One thing we can say is that somebody has carried a grenade or similar item illegally,” he said, adding that police were investigating.

Seven army and five air force personnel, along with seven civilians, were injured in a fire following the blast on the bus, operating between the Jaffna peninsula in the north of the island to the central town of Diyathalawa, he said.

Jaffna was part of the northern heartland of ethnic minority Tamils, who battled the government for a separate state for 26 years until their defeat May 2009.