BANGKOK — Five grenades exploded in the heart of Bangkok’s business district on Thursday evening, killing at least one person and wounding 75 as rival groups of protesters demonstrated and shouted insults at one another across a makeshift barricade.

The explosions, several of which took place on the platform of an elevated train, scattered shrapnel through crowds that included foreign tourists, sending people fleeing in panic into shops and restaurants.

The attacks threatened to ignite wider violence after more than six weeks of protests that seek to bring down the government and force a new election.

Deputy Prime Minister Suthep Thaugsuban, speaking on television, blamed the antigovernment protesters known as the red shirts, who have paralyzed parts of Bangkok. He said that rocket-propelled grenades had been fired from within an area the red shirts occupied. Although he said three people had been killed, the government’s Erawan Medical Center confirmed only one death.