DHAKA (AFP) - The Bangladesh police on Monday removed stringent security stationed around opposition leader Khaleda Zia's office in Dhaka, ending her forced confinement after 16 days, amid renewed deadly political unrest.

The authorities had ordered the former two-time premier confined to her office to prevent her spearheading anti-government protests as part of opposition efforts to force the downfall of Prime Minister Sheikh Hasina.

"We've withdrawn the additional security from her office after midnight," local police chief Rafiqul Islam told AFP, adding that Ms Zia was now free to leave. Two police vans and a water cannon parked outside Ms Zia's office in Dhaka's upmarket Gulshan district have also been removed, he said.

The siege at her office sparked a renewed upsurge in political unrest around the country that left 27 people dead.

Ms Zia called a nationwide transport blockade during the siege, with opposition activists firebombing buses, cars and lorries and police retaliating by firing bullets and tear gas.

A spokesman for Ms Zia's opposition Bangladesh Nationalist Party (BNP) confirmed that police had withdrawn from her office overnight but vowed to continue the transport blockade.

"At the moment, there is no security outside her office," Mr Sayrul Kabir Khan said.

Ms Zia wants Ms Hasina to call fresh elections after last year's controversial poll boycotted by opposition parties and marred by deadly violence.

The boycott meant most members of the 300-seat Parliament were returned unopposed, handing Ms Hasina another five years in power.

Ms Zia has also demanded the release of opposition officials and leaders detained in a crackdown against the latest violence. The BNP says at least 2,000 of its activists have been arrested.

On Monday, the police arrested Mr Nadim Mostofa, a BNP leader in the north-western city of Rajshahi.

As part of the crackdown, the authorities have blocked smartphone messaging services Viber and Tango to prevent protesters from coordinating attacks.

Ms Hasina has accused bitter rival Ms Zia of trying to trigger "anarchy" and ordered the security agencies to hunt down the protesters behind the firebombings.

Facing relentless opposition protests, Ms Hasina's government has also threatened to bring murder charges against Ms Zia for inciting violence.

Ms Hasina and Ms Zia, who have between them ruled Bangladesh for most of the last three decades, have a notoriously poisonous relationship.

The United States, Britain and the European Union have expressed concern over the latest unrest with the European Union, the nation's biggest export destination, urging Ms Hasina's government and the opposition to hold talks to resolve the crisis.