At least 18 people were injured in a blast by a railway track in the Sri Lankan capital on Wednesday, the military said.

The blast came over a week after eight people were killed and 73 injured when a bomb exploded on a train during rush hour in Colombo.

Doctors said 18 people were admitted to hospital on Wednesday.

"All of them were out of danger," said Dr. Wilfred Kumarasiri, director at the Kalubovila Teaching Hospital.

The explosion in Wellawatta, a suburb of Colombo, comes amid daily land, sea and air attacks in a bloody civil war that has killed more than 70,000 people.

The military said the bomb was planted along a portion of the rail track.

"It is too early to predict exactly, but it has to be a LTTE attempt, no doubt about it," said Lakxman Hulugalla, Director General at the Media Centre for National Security, referring to the Liberation Tigers of Tamil Eelam rebels.

Reuters witnesses reported slight damage to the railway track and minor damage to two train compartments.

The explosion came a day after Tamil Tiger rebels blamed the military for a roadside blast that killed six civilians in the far north.

The rebels, who are fighting for an independent state in the north and east, were not immediately available for comment but usually deny involvement in such attacks.

Analysts say the military has the upper hand in the latest phase of the long-running war given superior air power, strength of numbers and swathes of terrain captured in the island's east. But they still see no clear winner on the horizon.