BBC News, Hanoi
An unexpected amnesty for prisoners has been announced by Vietnam's government.
Vietnam hopes to have normalised trading relations with the US
The amnesty will take place just days before crucial votes on trade are held in the US Congress, and ahead of a visit by President Bush to Hanoi.
The communist authorities have been under pressure from rights activists to release all political prisoners before the US normalises trade relations.
But being released from prison does not necessarily mean freedom for critics of the government.
Vietnam usually grants amnesties to well-behaved and repentant prisoners twice a year - for national day in September and the Tet holiday in January.
This year it will hold another, at the end of October.
Deputy Prime Minister Truong Vinh Trong said it was simply to clear up any outstanding cases. But the timing seems fortuitous.
The US Congress is being asked to vote on what are called permanent normal trade relations (PNTR) two weeks later.
Just after that, President Bush will make his first visit to Vietnam to attend the Asia-Pacific Economic Summit.
In previous amnesties, a few of what the government calls "sensitive cases" have been included among several thousand released prisoners.
However they have usually then been subjected to house arrest and extensive surveillance and barred from contacting journalists.
There are no accurate figures for the total number of "sensitive cases" but human rights campaigners talk of around 400 currently in jail.
Many of these are members of evangelical Christian sects among hill tribes in the central highlands who oppose the government.
A minority are campaigners for multi-party democracy and other critics of the communist authorities.