Police opened fire Monday on Tibetan pro-independence protesters and reportedly killed at least four in the second day of violence in the Tibetan capital, foreign travelers said.

The reports from Lhasa were not immediately confirmed by official media, which reported 11 people killed in street clashes in the Tibetan capital Sunday.Police stationed on rooftops in Lhasa's main square fired down into crowds of Tibetans at about 5 p.m., a traveler from New Orleans said in a telephone interview.

He said he arrived on the scene shortly after the shooting and was told by Tibetans that at least two people were killed.

A second American, also speaking on condition of anonymity for fear of police reprisal, said he saw police open fire several hours later on about 40 Tibetans who were marching toward the main square.

He said he did not see marchers fall, but said Tibetans told him two were killed.

China's official Xinhua News Agency said earlier that one policeman and 10 Tibetans were killed Sunday in clashes in Lhasa, while 40 police and more than 60 Tibetans were injured.

Another American said many Tibetans reported Sunday's death toll was closer to 30, but there was no way to confirm that.

Foreign travelers in Lhasa said police showed restraint throughout most of Monday as thousands of Tibetans marched through the streets chanting pro-independence slogans and hurling goods looted from Chinese-owned stores onto bonfires.

The clashes were the fourth time in 18 months that tensions have boiled over between Tibetans and Chinese, who rule the remote southern region.

At least 40 were killed in the earlier clashes, including 24 who died one year ago during a daylong battle.

Sunday's protest was begun by Buddhist monks and nuns who apparently were marking that anniversary.

Protesters Monday stoned any Chinese who tried to bicycle through the area and dragged some from their bikes, the witnesses said.

A second American said he saw a policeman dragged from his bike and chased down the street at knifepoint.

"The streets are thick with people. There's lots of whooping and shouting and throwing stones. There's no control whatever," said an Australian. He said the protesters set up barricades with tables and garbage cans on some streets.

Tibet remains largely closed to journalists and the only independent reports came from travelers, many of whom who spoke on condition of anonymity for fear of police reprisals.

Xinhua said Sunday's violence began at noon when 13 monks and nuns paraded illegally through the Barkhor, the city's central market and location of its main temple, the Jokhang. They waved banners and shouted "Independence for Tibet," the report said.

They were joined by several hundred people, who stoned a nearby police station.

A Swedish traveler, who gave his name only as Pontus, said he ran to the roof of the Jokhang Temple for a better view.

"There were six people to the left of us taking pictures of the crowd ... Then they dropped their cameras and started firing with hand guns into the crowd," Pontus said. He said no warning was given.

He said he and four companions, some of whom took pictures of the shooting, later had their cameras and passports confiscated.