TAIPEI -- Taiwan police on Friday said a train explosion that left 25 injured late Thursday was a sporadic criminal case rather than a terror attack.

No relevant information was received prior to the blast and no group has claimed responsibility, a railway police officer surnamed Wang said at a press conference on Friday morning.

The explosion happened in a car on commuter train number 1258 between Hsinchu and Keelung as it was approaching Songshan railway station at about 10 p.m. Thursday. A fire broke out after the blast. It was put out within several minutes.

Twenty-five people were injured, including five in serious condition. The injured were rushed to six hospitals for treatment.

Police found a broken steel tube at the scene believed to have contained black powder, suggesting that it was a homemade explosive device, said Wang, adding police have obtained information about several suspects.

Three people with minor injuries left the hospital Thursday night, said Hong Shih-chi, deputy head of Taipei City Hospital Zhongxiao Branch.

The other three who remain in the hospital include a 14-year-old boy who sustained serious burns to his arms, legs and face, Hong told Xinhua. The boy is in the intensive care unit.

Security measures have tightened at train and subway stations on the island.