DHAKA - A firebomb attack on a bus killed four people Wednesday, including a young child, while an aide to opposition leader Khaleda Zia survived an assassination attempt in a new upsurge of political unrest in Bangladesh.

The attack on the bus in the northern town of Mithapukur was carried out as anti-government activists tried to enforce a transport blockade as part of efforts to force the downfall of Prime Minister Sheikh Hasina. It was the deadliest incident since an outbreak of violence at the turn of the year when Bangladesh Nationalist Party (BNP) leader Zia was confined to her office after calling for Hasina to stand down. Zia remains stuck in the compound.

The police chief in Mithapukur, Rabiul Alam, said the packed bus was firebombed as it travelled to the capital Dhaka, blaming the attack on followers of an Islamist party which is part of a BNP-led alliance. ‘At least 14 people were burnt in the attack. Four of them died, including a child whose body was charred beyond recognition,’ Alam told AFP. ‘Three of the victims are in a very critical condition.’  Eight activists from the radical Jamaat-e-Islami party had been arrested over the attack, Alam added. The BNP has denied that any parties in its opposition alliance were involved in the bus attack. In Dhaka, police confirmed that Riaz Rahman, a state minister for foreign affairs when Zia was premier, had been seriously injured Tuesday night after unidentified attackers shot at him. ‘He was shot four times from close range by at least three unidentified attackers. They also firebombed his car. His condition is now stable,’ Dhaka police inspector Rafiqul Islam told AFP.

The 74-year-old Rahman has been advising Zia since 2007. In the past week, unidentified attackers have firebombed the houses of several of Zia’s aides. The bus attack took the death toll in the latest unrest to 17 with hundreds more injured. Zia ordered the blockade last Tuesday as part of a campaign push to force Hasina to stand down in favour of a neutral government that would organise fresh elections. She blamed the government for the attack on Rahman, terming it ‘an act of cowardice and terror.’ In protest, her party called a nationwide strike on Thursday.

In a statement the United States said it was ‘shocked and saddened’ by the attack, calling it ‘outrageous and cowardly’. ‘We call on all parties to exercise restraint and eschew violence and intimidation, and we urge the government to ensure people can freely exercise their right to peaceful political expression,’ it said. British High Commissioner to Bangladesh Robert Gibson expressed concern at the violence and urged all parties ‘to come together in a dialogue to break the cycle of violence and disruption’. Moreover, Bangladeshi authorities deployed more than 8,000 security guards along the country’s rail network on Tuesday to try to halt a spate of train derailments by anti-government protesters.

A spokesman for state-owned Bangladesh Railway said the guards had been deployed to prevent saboteurs from removing ‘tracks and fishplates’ on main inter-city routes on the eighth day of a transport blockade. ‘Six trains have been derailed since the opposition blockade began,’ spokesman Syed Zahrul Islam told AFP.

, adding that more than a dozen people had been injured in the derailments.

‘As a result, we have no option but to deploy 8,328 (guards) across the network to prevent further acts of sabotage.’ The blockade began on January 6 as part of a campaign of protest by the main opposition Bangladesh Nationalist Party designed to force the government to hold fresh multi-party elections.

BNP leader Khaleda Zia, who boycotted a general election last year over fears it would be fixed, is currently confined to her office as Prime Minister Sheikh Hasina tries to prevent her from spearheading the protests. Zia’s spokesman said on Tuesday the BNP leader had no intention of softening her demands in order to secure her release from the office, where she has effectively been a prisoner since January 3. ‘She won’t halt protests until the government agrees to hold election under a neutral administration,’ Shimul Biswas told AFP by phone from inside Zia’s leadership compound in Dhaka’s upmarket Gulshan district.

Local media said thousands of paramilitary border guards were also being deployed to enhance security in 22 districts that have been roiled by unrest. Biswas said at least 2,000 BNP supporters and officials have been detained in the last two weeks. On Monday police arrested five senior officials including its publicity secretary Habibur Rahman from outside a private television station where he was a guest on a talk show.  Hasina has accused Zia of trying to trigger ‘anarchy’. At 11 people have been killed and hundreds of buses and trucks torched or damaged since the unrest began at the turn of the year.