They put pressure on people, kept interrogating them, they used physical violence... under this pressure, some people moved out of the country

Czech prosecutors

Jaromir Obzina, 72, and four other officials are accused of running a campaign of physical intimidation against the signatories of the Charter 77 human rights manifesto.

They all deny the charges, but if convicted, face prison sentences of up to 10 years.

The trial is one of the Czech Republic's biggest against former communist officials, and is expected to continue until 11 December.

Exiled

Mr Obzina is accused of launching an operation code-named "Sanitation" to force anti-communist opponents flee the country.

President Havel was also targeted

The operation focused on around 50 dissidents, who were subjected to threats and interrogations.

Fear for their life forced around 20 of them to flee the country.

The Czech President, Vaclav Havel - a leader of the "Velvet Revolution" which toppled the communist rule in 1989 - was also on the list at the time.

But he stayed in the country and was later imprisoned.

The spokesman for the prosecution said that another 13 former officials could be charged in connection with the case.

Several low-ranking secret service agents have already been convicted and given suspended sentences for beating up dissidents and forcing people out of the country.

But unlike some of its neighbours, the Czech Republic have been slow to address crimes committed under communist rule.

Last month the authorities charged former Prime Minister Lubomir Strougal with preventing an inquiry into secret police activities.