The police opened fire on protesters in southern Myanmar on Sunday, as the military regime began what appeared to be its toughest crackdown yet on the demonstrations against its month-old coup. At least three people were killed, two doctors said.

More than 50 other people were wounded in the shooting in the city of Dawei, said Dr. Tun Min, who was treating the injured at a local hospital and who confirmed the three deaths. A second doctor, who asked not to be named for fear of retaliation, also said that three people had been killed.

Witnesses said the police opened fire on the crowd in Dawei, which they said numbered in the hundreds. The police also used tear gas in an attempt to break up the protest, the witnesses said.

The security forces were also cracking down Sunday on other protests around the country, including in the largest city, Yangon, where hundreds of people were arrested.

The deaths in Dawei brought the number of people shot and killed in the protests to at least six since the Feb. 1 coup, which ousted the civilian government led by Daw Aung San Suu Kyi, Myanmar’s most popular politician.