BANGKOK — Thai armored vehicles on Wednesday morning rammed through the barricades put up by antigovernment protesters, and infantry troops stormed into the protest zone, as the government moved aggressively against demonstrators who have occupied Bangkok’s central retail district for more than six weeks.

Troops took control of key roads as well as a large park in the protest zone. Television footage showed soldiers opening fire at the back of protesters, who were running for cover. A government spokesman, Panitan Wattanayagorn, said the first phase of the operation had been "successful."

“We are going to focus on setting a perimeter,” Mr. Panitan said on television. “We would like to reassure the citizens, the residents of Bangkok, that the operations are designed to make sure we stabilize the area.”

Several fires raged around the protest zone, including what appeared on television to be a blaze engulfing a large block of buildings. The zone itself is among the wealthiest neighborhoods in Bangkok and includes many corporate headquarters, high-end shopping malls, luxury hotels and high-rise apartment buildings.One of the protest leaders, Weng Tojirakarn, appeared calm even as the operation was under way. “I have no gun,” he said in an interview inside the encampment. “I can’t do anything.”