Traders in Assam's main city of Guwahati downed their shutters just before dusk with police and paramilitary troopers coaxing shopkeepers to wind up their business for the day.

"The city was almost dead even before sundown. Some traders who were a bit late in closing down their shops were asked by police to hurry up," said Sunil Das, a garments dealer in the busy Fancy Bazar market here.

The state government in an order directed all traders in the city to close down their businesses by 5.30 p.m. each day until further instructions, following serial bombings in the state including three powerful explosions in Guwahati in the past four days.

"Militants often take advantage of darkness to trigger explosions or launch grenade attacks in crowded areas. The decision to shutdown businesses after dusk is part of safety measures," Guwahati Municipal Corporation spokesman Binod Hazarika said.

Earlier Wednesday, paramilitary troopers killed three traders mistaking them to be militants, while there was yet another powerful explosion in eastern Assam's Tinsukia district.

A police spokesman said troopers of the Central Industrial Security Force (CISF) asked three youths riding a motorcycle to stop at a check point near the eastern Geleki town, 370 km from Assam's main city of Guwahati.

"The youths took some time to stop their motorbike and in the meantime CISF troopers opened fire at them killing two on the spot. Another died in a hospital," a senior police official said by telephone.

The state government has ordered an enquiry by a magistrate into the killing of the civilians after locals identified the three youths as traders and not linked to any rebel group.

"A case of murder has been registered and investigations are on. The law will take its own course," the official said.

Meanwhile, an explosion took place in Tinsukia district Wednesday although no one was injured.

"The blast took place in an isolated area with no casualties reported," Tinsukia district magistrate Absar Hazarika told IANS.

Fear and panic has gripped people across Assam after the renewed violence.

"Everybody is avoiding going out after dusk as you never know what happens. The frequent bombings have led to panic," Monimala Baruah, a housewife, said.

On Tuesday night, separatist guerrillas shot dead a ruling Congress party leader near Naharkatia in eastern Assam.

The outlawed United Liberation Front of Asom (ULFA), a rebel group fighting for an independent homeland since 1979, last week threatened to kill Congress party workers and leaders if New Delhi did not stop a military offensive launched against the outfit immediately.

There were five explosions Tuesday, including a blast on a goods train, killing one person and injuring 20.

The blast Wednesday was the 13th explosion in the past week with 10 people being killed and 62 wounded in the earlier blasts in this oil, tea and timber-rich state.

The bombings were preceded by the slaughter Jan 5-8 in eastern Assam by separatist guerrillas of 73 people, 61 of them Hindi-speaking migrants.

The latest attacks were Assam's worst violence in years, and came after New Delhi called off a six-week ceasefire in September and resumed military offensives blaming the ULFA for stepping-up violence and extortions.

The ULFA did not claim responsibility for any of the attacks. More than 10,000 people have lost their lives to insurgency in Assam during the past two decades.