Wed Sep 26, 1:39 PM ET

NEW YORK - The United States said Wednesday it was "very troubled" by Myanmar's deadly crackdown on anti-government protesters and urged "a peaceful transition" in Yangon from military rule to democracy.

"The United States is very troubled that the regime would treat the Burmese people this way. We call on the junta to proceed in a peaceful transition to democracy," said White House national security spokesman Gordon Johndroe.

Asked whether Washington considered earlier reports of violence in Myanmar to have been confirmed, Johndroe replied: "Yes."

Myanmar security forces used batons, tear gas and live rounds Wednesday in a violent crackdown on mass protests against the military junta, killing at least four people including three Buddhist monks.

Up to 100,000 people defied heavy security to take to the streets of the main city Yangon, marching and shouting abuse at police despite blunt warnings from the ruling generals who are facing the most serious challenge to their rule in nearly two decades.

Two of the monks were beaten to death while another was shot when he tried to wrestle a gun away from a soldier and the weapon discharged, two senior Myanmar officials told AFP.

They said the monks were killed near Yangon's Shwedagon Pagoda, Myanmar's holiest site and a key rallying point for the clergy leading the nine days of protests which have spread across the Southeast Asian nation.

A fourth man, who was not a monk, was shot dead, a hospital source said.