Cold War documents released this week show that Soviet leaders were so worried about the 1968 Prague Spring reform movement in Czechoslovakia that they sent experienced KGB spies to help thwart it, a researcher said Thursday.

On the orders of KGB head Yuri Andropov, 15 agents came in May 1968 to target Czechoslovakia's intellectual elite, a major force behind attempts to reform the communist regime in the 1960s.