Tens of thousands of students have protested since last Sunday when a privately run bus hit and killed the students, alarming the government ahead of a general election this year .

Several thousand students took to the streets for an eighth straight day on Sunday. Police fired tear gas at protesting students to disperse them from different points of the city.

"Our police force has started a week-long drive to bring discipline on the roads," Prime Minister Sheikh Hasina said at an event in Dhaka on Sunday.

Spontaneous student protests are rare in Bangladesh, and Hasina suggested her political rivals were using the issue to stir up anti-government sentiment. The opposition Bangladesh Nationalist Party denied any involvement in the protests.

On Sunday, students blocked roads and disrupted traffic, although they maintained emergency lanes for ambulances and other emergency vehicles.

Home Minister Asaduzzaman Khan on Sunday warned that action would be taken against them if their protests become too disruptive.

"Everything has an optimum point, and if anyone crosses the limit action will be taken ... so don't cross the limit," he said inaugurating traffic week in the city.

Separately, the US embassy said in a statement outgoing envoy Marcia Bernicat's vehicle was attacked by armed men, some on motorcycles, in Dhaka on Saturday.

"The ambassador and her security team departed the area unharmed ... however, two security vehicles sustained some damage," it said in the statement issued on Sunday.

Police said they had not identified the attackers.

The protests spreading across Bangladesh have highlighted traffic risks in the densely populated country, where more than 4,000 people die in road accidents each year, one of the world's highest rates, the World Bank says.