BANGKOK — A renegade major general who allied himself with the protesters who have paralyzed Bangkok for weeks was shot in the head and critically wounded here on Thursday as the military began sealing off a barricaded encampment of antigovernment protesters.

The general, Khattiya Sawatdiphol, 58, had become a symbol of the lawlessness and impunity that have torn Thailand apart as the protests have pitted the nation’s poor against its establishment.

He was shot during an interview with a reporter for The New York Times about 7 p.m., one hour after the military announced the start of a blockade and cut off electricity and water to a tent city of thousands of protesters.

The reporter, who was two feet away and facing the general, heard a loud bang similar to that of a firecracker.