Imphal: Three people were killed and four others injured when a powerful blast rocked Manipur's capital city Imphal Sunday, police said.

"An IED (improvised explosive device) that was planted by the roadside near Khuyathong area, close to Imphal market, exploded at 6 a.m., killing three migrant labourers on the spot and injuring four others," a police official said.

He said the labourers, all non-Manipuris, gathered for tea in Khuyathong, which is about one km from Imphal city police station, when the blast took place. Labourers - identified as Shiv Yadav, 35, Lalan, 35, and Kusum Pandit, 60 - were working as load men in the area, he said.

The official said the injured have been rushed to the Regional Institute of Medical Science and Hospital here. Their medical condition is stated to be critical. Senior police officials along with additional security forces have rushed to the spot and launched a combing operation to arrest those responsible for the explosion.

No militant group has yet claimed responsibility for the blast. Chief Minister Okram Ibobi Singh and Deputy Chief Minister Gaikhangam Gangmei, who holds the home portfolio, visited the injured at the hospital.

Condemning the incident, the chief minister said adequate compensation would be paid to the families of those killed and the government would bear the expenditure for treatment of those injured in the blast. Gangmei said: "It was a cowardice to attack the unarmed innocent people, to disturb the peace and harmony."

With Sunday's incident, the number of non-Manipuris killed in the state this year has gone up to nine. This is the third such incident within less than a month in Manipur. Two youths were killed and four others injured when militants triggered a bomb blast in a market in Imphal Dec 15. A 10-year-old boy was killed in a blast Nov 29, a day ahead of Prime Minister Narendra Modi's visit to the state.