PARIS — Japan issued a travel alert for Europe on Monday, joining the United States and Britain in warning of a possible terrorist attack by al-Qaida or other groups, but tourists appeared to be taking the mounting warnings in stride.The Foreign Ministry in Tokyo urged Japanese citizens to be cautious when using public transport or visiting popular tourist sites — issuing another blow to Europe's tourism industry, which is just starting to recover from the global financial crisis.RELATED:US warns Americans to be vigilant when in EuropeUS officials: Bin Laden involved in European terror plotEuropean authorities — especially in Britain, France and Germany — tightened efforts to keep the public safe in the wake of warnings by officials that the terrorism threat is high and extra vigilance is warranted.Last week, a Pakistani intelligence official said eight Germans and two British brothers were at the heart of an al-Qaida-linked terror plot against European cities, but the plan was still in its early stages, with the suspects calling acquaintances in Europe to plan logistics. The official said the suspects were hiding in North Waziristan, a Pakistani tribal region where militancy is rife and where the US has increased its drone-fired missile strikes in recent weeks.Security officials say terrorists may be plotting attacks in Europe with assault weapons on public places, similar to the deadly 2008 shooting spree in Mumbai, India. European officials have provided no details about specific targets.On Monday, French police arrested a 53-year-old man suspected of links to a bomb threats including one Friday at a Paris railway hub, an official with knowledge of the investigation said on condition of anonymity. The suspect, who was not identified, was detained southwest of the capital for possible links to a phone-in threat at the Saint-Lazare train station. French authorities recorded nine bomb alerts in the capital in September, including two at the Eiffel Tower — a threefold increase from a year earlier. No explosives were found.The US State Department alert Sunday advised the hundreds of thousands of American citizens living or traveling in Europe to take more precaution about their personal security. The British Foreign Office warned travelers to France and Germany that the terror threat in the countries was high.Business travelers and tourists arriving Monday at Paris' Charles de Gaulle airport from the United States said they were aware of the new warnings but weren't changing their plans.