More than 7,000 people have been detained in the country's worst bout of political violence since national elections a year ago in which the ruling Awami League was re-elected after a boycott by the opposition, Guardian reported on Friday. The latest protests have been called by Khaleda Zia, leader of the opposition Bangladesh Nationalist party (BNP), who wants Sheikh Hasina, the prime minister, to resign and call fresh elections. Hasina has said her government will remain in office until her term ends in 2019.

After a year of relative calm, there are fears that the violence may intensify as it did in 2013, when clashes between the parties' supporters left nearly 300 people dead. Many of the casualties this week have been caused by arson attacks on buses. A survivor of one attack, Rajib Karmokar, said he had been accompanying a friend to complete paperwork at his college in Dhaka when petrol bombs hit their bus.

"I was on the aisle side of the bus in the last row. There were about 60 passengers in the bus. Miscreants stopped the bus, broke the windows and, then hurled petrol bombs," said Karmokar, 22, who was being treated for burns to his face and hands at Dhaka medical hospital.

Authorities have banned motorcyclists from carrying passengers in an attempt to halt a spate of drive-by firebomb attacks. The smartphone messaging service Viber has been banned after it became a popular communication medium for anti-government protesters. Both the government and the opposition, which is allied to the Islamist Jamaat-e-Islami party, had planned rallies on the anniversary of the election, but police banned both. When Zia was confined to her office after she attempted to visit her party headquarters, she announced a blockade on all transport across the country. There have also been closures of all shops and businesses.

Selima Rahman, vice-chair of the BNP, said the blockade had been declared because the government "did not allow any democratic space for the opposition".Rahman said: "The election was a farce. The government at the time said they did the election to protect the principle of the constitution. This movement will continue until a fresh election is declared."

Tensions have been heightened by death sentences passed on leading Islamists over their role in the 1971 independence war.

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