Paramilitary and plainclothes police blanketed the Tibetan capital with patrols and checkpoints on Saturday, imposing what witnesses called a tense calm on the first anniversary of a violent anti-Chinese riot.

Lhasa residents said police with rifles or batons marched around the Jokhang Temple and the adjacent Barkhor Square in the old city, where protesters ran rampant last year. A Hong Kong tourist said two military helicopters hovered over the city on Saturday morning — a rare sight — and that officers demanded to see identification at checkpoints.

“I was constantly stopped for identity check in the past few days,” said the tourist, who only wanted to be identified by his surname, Chu, because of the heavy security. “I was stopped twice last night on my way back to my hotel from dinner.”

The Communist Party secretary of China’s Tibetan Government defended the troop presence as necessary to quell any separatist violence.