PRAGUE (AP) — A ceremony to honor the victims of the 1968 Soviet-led invasion of Czechoslovakia on Tuesday turned into a protest against Czech Prime Minister Andrej Babis.

Hundreds jeered and booed Babis' arrival for a ceremony in front of the Czech public radio building in downtown Prague, a site of a fierce street battle between unarmed civilians and invading troops in the first hours of occupation where 17 people died.

"Shame, shame...," the crowd chanted while blowing horns and whistles during his speech.

Babis didn't immediately react to the protest.

Babis, a populist billionaire, is a controversial figure because of a power-sharing deal with the maverick Communist Party and fraud charges he is facing. His position is also complicated by allegations he collaborated with the former communist-era secret police.

Troops from the Warsaw Pact, a military alliance formed in 1955 between the Soviet Union and seven Eastern European nations, invaded Czechoslovakia on Aug. 20, 1968 to crush liberal reforms enacted in the brief era known as the Prague Spring. The country was subsequently taken over by a hard-line Communist regime fully loyal to Moscow.

In 1968 alone, 137 people were killed by Warsaw Pact soldiers, and a total of more than 400 died during the occupation of Czechoslovakia that ended only after the 1989 anti-communist Velvet Revolution.