Updated

Protesters have rallied in downtown Bangkok on Thursday on the eve of a key vote on a bill that would grant amnesty to leaders and others involved in often-violent political conflicts since 2004.

The Senate announced it would move up the vote to Friday from Monday in an attempt to ease rising tension over the bill, which has already passed the more powerful lower house.

The opposition Democrat Party and its supporters say the ruling party-proposed legislation is intended to whitewash former Prime Minister Thaksin Shinawatra's alleged crimes and allow his return from self-imposed exile.

The bill would also grant amnesty to Democrat leaders who face charges for their alleged role in protester deaths during a 2010 crackdown.