By Mainul Islam Khan

DHAKA, Bangladesh

 At least seven people have been killed when petrol bombs were hurled at a passenger bus in Bangladesh on Tuesday.

The bus was travelling along a highway linking Bangladesh's capital Dhaka and second city, Chittagong, amid a month-long transport blockade that opposition activists have allegedly enforced with frequent petrol bomb attacks. 

The police inspector of the local Chouddagram police station, Uttam Kumar Chakroborty, confirmed the attack.

Most of the burnt passengers were taken to the nearby Comilla Medical Hospital while seven, who had severe burns, were taken to the Dhaka Medical Hospital, said Partha Shankar Paul, the hospital's resident doctor in the burns unit. He said their condition is critical.

The bus was heading to Dhaka from Cox’s Bazaar, a coastal city that is Bangladesh's most popular tourist destination.

According to statistics from the local daily Prothom Alo, there have been at least 46 people killed in the past month, mostly in arson attacks on vehicles defying the transport ban. More than 800 vehicles have been set aflame or damaged during the blockade. 

A 72-hour nationwide shutdown began on Sunday, called by the opposition Bangladesh Nationalist Party. 

The Bangladesh Nationalist Party has enforced the indefinite transport blockade since Jan. 5 when the government allegedly prevented them from staging protests on the first anniversary of controversial January 2014 elections. 

The opposition claims that thousands of their activists have been arrested by police since Jan. 5 and accuse the police of carrying out extra-judicial killings of their supporters.