By Rob Cameron
BBC News, Prague
Czechs have staged another protest against US plans to build a radar station in their country as part of a missile defence shield - and the issue looks set to overshadow US President George Bush's visit to Prague on 4-5 June.
The US says expanding the defence system will protect both America and Europe from any attack by Iran or other so-called "rogue states".
The rally was not large - but polls show most Czechs oppose the base
But the Czech government, which has launched formal talks on the base with Washington, appears to be having difficulty persuading its citizens.
Neighbouring Poland - set to host US interceptor rockets - has seen similar protests.
Demonstrations in the Czech Republic usually conform to three fundamental rules: they are rarely large, they are almost never violent and they are often surreal.
Saturday's protest - organised by a group called "No to Bases" - was no exception.
Barely 2,000 people - in a city of 1.2 million - attended the protest. It passed off peacefully, with the exception of a brief shouting match as angry taxi drivers attempted to force their way through the crowd. And jumping up and down a few metres away was a group of young anarchists, dressed as circus clowns.
But it would be foolish to dismiss the demonstration - the last scheduled protest before President Bush arrives in Prague - as irrelevant.
Participants came from various walks of life and had little in common politically or culturally. Young Greens stood alongside members of the far-left Union of Communist Youth. Pensioners mingled with punks. Parents stood and listened to speeches as their children clutched ice-creams in the sun.
Several well-known opposition politicians also attended the protest.
"I particularly support the idea that we should have a referendum," the country's former Foreign Minister Jan Kavan told the BBC.
It was Jan Kavan who signed the North Atlantic Treaty on 12 March, 1999, in Independence, Missouri. It formally brought his former Soviet bloc country into the Nato alliance.
Mr Kavan, a member of the opposition Social Democrats who has largely withdrawn from mainstream politics, opposes what he sees as the centre-right government acting against the wishes of its people.
"To install American military bases here without asking the population their opinion on such an important matter is contrary to my perception of democracy," Mr Kavan said.
There was no referendum on Nato membership. However, joining the alliance was a political priority for every post-communist Czech government and opinion polls showed overwhelming support for the idea.
Missile defence is rather different.
Almost every public survey conducted in recent months has shown around 60% of Czechs opposed to the radar base. According to the country's leading polling agency STEM, those "strongly against" far outweigh those "strongly in favour".
Their opposition rests on a number of concerns, including fears of needlessly antagonising Russia, turning the country into a potential terrorist target, and exposing people living near the base to dangerous levels of radiation.
The US plan is politically risky for the Czech PM
Prime Minister Mirek Topolanek rejects all those claims.
"The radar base will have no negative effect on the population in the surrounding villages," he told reporters. "There will be no threat to human health, no effect on the quality of their lives or that of the environment."
That message of reassurance has been echoed by other Czech officials, as well as the US ambassador in Prague. But it does not seem to be sinking in.
So one week before President Bush arrives in Prague, Mr Topolanek is in a tricky position. The left-wing opposition is clamouring for a referendum on the base, mindful of the fact that Czechs seem to be against it.
The opposition lacks enough MPs to force a popular vote. But stationing the US base on Czech soil must be approved by parliament, where Mr Topolanek has no guaranteed majority.
A vote on hosting the base will not take place for at least a year, but the Czech prime minister risks giving Mr Bush a political promise he cannot fulfil.
His government only exists thanks to two renegade MPs from the opposition Social Democrats, who left the chamber during a vote of confidence in January. But their support for the radar base is far from automatic.
The issue is also causing considerable friction inside the Green Party, a small but crucial member of Mr Topolanek's coalition. Several members of the party attended Saturday's demonstration, earning them a sharp reprimand from the party's chairman.
The "No to Bases" initiative, meanwhile, has announced more demonstrations to coincide with Mr Bush's visit.
Those demonstrations might not be huge. They might not be violent. There may well be clowns. But if the American president fails to persuade Czechs of the benefits of missile defence, it could be the clowns who have the last laugh.