Japan urged its nationals to avoid wearing the politically charged colors of red or yellow in Bangkok, while France and Britain advised citizens to stay indoors as rioting spread Monday in the Thai capital and countries worldwide issued travel advisories. Americans were urged to "exercise caution" in Bangkok and South Korea called on its citizens in the Thai capital "to return home (to Korea) if they are not on urgent matters." A violent showdown between soldiers and anti-government protesters flared in more than a dozen parts of central and northern Bangkok, as the protesters burned public buses and set tires on fire that sent plumes of black smoke into the sky. Troops in combat gear fired repeated volleys - mostly in the air - in efforts to restore order during a full-day of cat-and-mouse chases with the red-shirted mobs. More than 70 people were injured. The protesters are demanding the resignation of Prime Minister Abhisit Vejjajiva. On Sunday, a group of protesters viciously attacked Abhisit's car by hurling chucks of concrete and metal barricades at his armored vehicle, before he was able to escape. They wear red to distinguish themselves from rival protesters, who dress in yellow. "We recommend you should avoid wearing red or yellow shirts," Japan's Foreign Ministry urged citizens in a statement that also advised nationals living or traveling in Bangkok not "to comment on politics." The US Embassy issued a warden message urging Americans "to avoid the areas of demonstrations and to exercise caution anywhere in Bangkok." Thailand's government spokesman Panitan Wattanayagorn repeatedly appeared on national television Monday, at times speaking in English, with updates on the security situation. "We must protect foreign tourists," the government spokesman said, urging Thais to help keep foreigners up to date on the crisis as some areas cleared of clashes and new ones arose. "If you have foreign friends, please help them." Many of the Bangkok's major shopping malls closed Sunday and remained shut Monday. "The French Embassy strongly recommends that French nationals stay in their homes or hotels," said a statement on the embassy's Web site that also recommended postponing nonessential travel until calm returns. Britain told citizens to "urgently review" travel plans to the Southeast Asian nation and "to avoid any areas where demonstrations are taking place and to stay indoors as far as possible." Australia advised its nationals to reconsider traveling to Bangkok or surrounding provinces, and to "exercise a high degree of caution because of the political instability in Thailand and the possibility of political demonstrations." "The Australian government is deeply concerned at developments in Thailand," Foreign Minister Stephen Smith told reporters. "We urge the political leadership in Thailand to resolve these matters peacefully and in accordance with the law." Anti-government protesters began a sit-in outside the prime minister's office March 26, reviving the country's protracted political turmoil. The protests turned violent over the weekend when protesters stormed the venue of a summit of Asian leaders in Pattaya, about 60 miles (100 kilometers) south of Bangkok, prompting Thailand to cancel the summit and evacuate the leaders by helicopter. Several countries whose leaders were airlifted out of the summit advised citizens to postpone travel, including Singapore, the Philippines and Malaysia, while China warned citizens "to exercise caution" in Thailand. The rioting comes just months after a rival group of yellow-shirted protesters shut down Bangkok's two airports during a weeklong shutdown that stranded more than 300,000 travelers.