Updated

Chinese authorities have allowed rowdy anti-Japanese demonstrations in several cities to defuse simmering public anger over a territorial dispute with Japan and to prevent the frustrations from being turned against the Chinese regime itself, analysts said Monday.

Thousands of Chinese joined in sometimes violent protests Saturday, hoisting signs protesting Japan's claim on what China calls the Diaoyu islands. Japan calls them the Senkaku islands.

On Monday, dozens of young men scuffled with police who were trying to contain protesters in the central Chinese city of Wuhan, news photographs showed. Hundreds of youth — mostly young men — marched with flags and signs, some of which called for a boycott of Japanese goods.

Japanese Prime Minister Naoto Kan said Monday that the protests were "regrettable." He said Japan asked China to ensure the safety and security of Japanese citizens and companies in China, and that the two countries must work "calmly" to improve ties.

China broke off ministerial-level contacts with Japan last month over Tokyo's detention of a Chinese fishing boat captain. Japan eventually released the captain, but Beijing shocked Tokyo by demanding an apology.

Earlier this month, the tensions seemed to ease after the prime ministers of the countries held an impromptu after-dinner meeting in the corridor of an Asia-Europe summit.

Tolerated by Chinese authorities, the demonstrations began peacefully but appeared to spin out of control with some marchers carrying crude, racist banners and even demanding a Chinese woman strip in public because her dress resembled a kimono. Later, the government warned the public to obey the law when expressing their nationalist feelings.

Japanese retailers Ito-Yokado and Isetan said protesters in the southwestern city of Chengdu broke windows and showcases in their stores, Kyodo News agency reported.

The website of the anti-Japanese China Federation for Defending Diaoyutai posted a photo that showed protesters in Chengdu holding a red and yellow canvas banner that called for Japan to be "wiped off the face of the earth." Others used English and Chinese profanities and urged violence against Japanese.

"Take a Japanese wife, then string her up and beat her everyday," read a sign held up by a young man and pictured on Gouride.com, a Chinese language web forum dedicated to anti-Japanese discussions.

Protests in China and online content are often quickly shut down or heavily controlled. Gouride.com is registered in the United States, but other sites based in China saw anti-Japanese comments and protest photos quickly deleted by censors.

It was not clear whether the organizers of the protests in Chengdu had permission to demonstrate. Hong Kong's Apple Daily newspaper said that they were organized by government-sponsored university groups.

A student at the Southwest University for Nationalities in Chengdu who would identify himself only by his online nickname, Break, said plans for the demonstration there were spread through online instant messaging groups but he was unclear about who had organized it.

Shi Yinhong, a professor of international relations at Renmin University in Beijing, said the students could not have taken part in the demonstrations if the government had opposed them.

"If the government very consciously opposed or didn't want these demonstrations, if they resolutely didn't want them, then there would be nothing," Shi said.

In Chengdu, a woman who was eating in a fast food restaurant along the demonstration route was forced to strip because marchers mistook her traditional Chinese dress for a kimono. She undressed in a bathroom and borrowed clothes from others, said the manager of the Dicos restaurant where the incident occurred. The man, who would only give his surname, Zhong, said he shut down the restaurant for a few hours until the marchers passed.

While allowing the demonstrations, the government also tried to quickly distance itself from the violence and offensive language of some protesters, posting a statement late Saturday that called for "rational" patriotism.

"It is understandable that some people expressed their outrage against the recent erroneous words and deeds on the Japanese side," Foreign Ministry spokesman Ma Zhaoxu said in an online statement. "Patriotism should be expressed rationally and in line with law."

Liu Shanying, an analyst at the Chinese Academy of Social Sciences' Institute of Political Science in Beijing, said the protests gave Chinese a chance to vent their anger toward Japan — before it turned into frustration with the Chinese government.

"The government knows that if they suppress public sentiments, it will only make them stronger," Liu said. "The government already has a bad reputation at home, given all its problems with corruption, bribery, high housing prices and pensions, etc."

"It has to allow the public to vent their anger toward foreign countries, otherwise the public would come to doubt the government's legitimacy," he said.

A man in the political department at Wuhan's Public Security Bureau said he had not heard anything about a protest Monday. Phones in the bureau's publicity department and general office rang unanswered.

China's state-run Xinhua News Agency said more than 2,000 people protested in Chengdu and thousands of college students gathered in the northern city of Xian.

The report was in English only. The protests were not reported in Chinese-language state media, and many comments and photos were quickly removed from mainland websites.