At least four more deaths have been reported in Bangladesh as riots continue to surge following the execution of top opposition leader, Abdul Quader Molla.

Prime Minister Sheikh Hasina vowed to crack down on the violence on Sunday as opposition supporters torched houses and fought battles with officers during a third day of unrest, police said.

At least 25 people have been killed in clashes involving opposition, pro-government activists and police since Thursday, when Jamaat-e-Islami leader, Abdul Quader Molla, was put to death for crimes committed during the nation's independence war in 1971.

Members of the Jamaat-e-Islami party said the execution was politically motivated.

Molla's hanging triggered fresh unrest in Bangladesh, which was already reeling from political violence in the build-up to a deeply divisive national election scheduled for January 5.

Warning signs

Independent United Nations experts Urged the Bangladeshi government to postpone Molla's hanging, citing concerns that he did not receive a fair trial, according to a UN press release.

"The execution of Molla could trigger further violence and unrest that has been agitating the country in the recent months,” said Christof Heyns, Special Rapporteur on summary executions in the UN press release.

Opposition parties have demanded that the government resign and hand over power to an independent caretaker to oversee January's vote.

Molla was one of five opposition leaders and other politicians sentenced to death by the International Crimes Tribunal, which was set up in 2009 to investigate crimes of genocide committed in 1971 during the Bangladesh Liberation War.

Some 250 people have been killed in street protests since January, when the first verdicts of the tribunal were handed down.

Source: Al Jazeera and agencies