Czech President Milos Zeman was booed as he addressed an event marking the 25th anniversary of the Velvet Revolution.
Hundreds of opponents of Zeman turned out for the November 17 event commemorating the end of communism in then-Czechoslovakia.
Demonstrators booed Zeman and threw apples and eggs at the Czech president, who has been criticized in his homeland for his pro-Russian stance and use of foul language in public.
One egg hit German President Joachim Gauck, who was a guest at the anniversary event along with the presidents of Hungary, Poland, and Slovakia.
Gauck was reportedly shaken by the incident momentarily but continued his participation in the celebrations.
Some protesters specifically mentioned Zeman's perceived pro-Russian stance as a reason they showed up to heckle the Czech president.
PHOTO GALLERY: Thousands of Czechs held symbolic red cards in the air on November 17, in a protest against President Milos Zeman. Protesters were angry with what they regards as Zeman's pro-Russian stance on EU sanctions on Russia, his criticism of the Russian protest-punk group Pussy Riot, as well as his use of vulgar language during a recent radio interview.
Earlier on November 17, Zeman gave an interview to a Russian TV channel saying that "there is simply a civil war in Ukraine" and calling Western sanctions on Russia a no-win strategy.
On November 17, 1989, a student protest in Prague was violently dispersed by police, triggering the peaceful collapse of communism in what was then Czechoslovakia.
As part of the celebrations, Czech Prime Minister Bohuslav Sobotka will fly to Washington to unveil a bust in the U.S. Congress of Vaclav Havel, the former dissident and president who led the protests against communist rule.
Havel died in 2011.
Unlike the Czech Republic, the anniversary is not a state holiday in Slovakia, although celebrations are scheduled there as well.
Based on reporting by Reuters, AFP, and CTK