Police in the Bangladeshi capital have fired rubber bullets at stone-throwing protesters taking part in a nationwide blockade to force electoral reform.
Clashes were reported across the capital, Dhaka
Several people were injured in clashes in Dhaka, local media reported.
The three-day blockade of roads, ports and railways is being organised by an alliance of political parties who want elections set for this month postponed.
The Awami League and its allies say they will boycott the 22 January poll, alleging it will not be free and fair.
Bangladeshi President Iajuddin Ahmed says the elections will go ahead as planned.
The BBC's John Sudworth in Dhaka says this is a constitutional crisis being played out on the streets.
Thousands of security forces were deployed in Dhaka for the first day of the blockade.
Police said protesters pelted them with rocks and stones. "Our officers shot tear gas and rubber bullets to disperse the mob," a police sub-inspector, Kankan, told the French news agency AFP.
The blockade has brought Dhaka to a standstill, with schools shut and vehicles absent from the streets.
Previous agitation over the issue has led to more than 30 deaths countrywide and the opposition parties say the protests will continue until their demands are met.
Awami League spokesman Abdul Jalil said: "We will not accept farcical elections. We will shut down the country for weeks if the government goes ahead with holding the elections."
But President Ahmed, head of the caretaker government, said the constitution demanded the polls be held within 90 days, and they would proceed.
The Bangladesh Nationalist Party (BNP)-led government handed power to the interim administration at the end of October.
The Awami League said more than 1,000 activists were detained ahead of the protests.
Its main demand is that the government use an updated version of the 2000 voter register, and not one created over the past few years.
The political bloc led by the BNP accuses the Awami League of "sensing defeat" and being determined to sabotage the elections.