American military experts have arrived in the Czech Republic to examine potential sites for a new missile defence base.
The US wants to expand its missile defence system
During a week-long mission they will inspect three training military grounds.
The United States is said to be considering either the Czech Republic, Poland or Hungary for the base.
Its purpose will be to shoot down long-range missiles before they reach their targets in the US or Europe.
The visit of the 22 American experts is the last stage in two-year long talks between defence officials of both countries, the deputy spokesman of the Defence Ministry in Prague, Jan Pejsek, told the BBC's News website.
It is part of the new security strategy adopted by the Czech government in 2004, he said.
American military experts have already been in Poland and are expected to go on a similar fact-finding mission in Hungary, the deputy spokesman said.
Czech authorities have stressed that the purpose of the nature of the visit is purely technical, and any decision to locate an anti-missile base would be a political one.
The base, designed to neutralise a missile attack on either the US or Europe, would employ up to 1,000 people, and though controversial, would bring substantial economic benefits to the host country.
However, the Czech Republic's chances to win the contract for the base are being damaged by the ongoing political stalemate, BBC's Rob Cameron reports.
It's seven weeks since inconclusive parliamentary elections and there's still no new government in Prague. With a decision on the new base due in September, time is running out.