An American missile strike killed five German militants Monday in the rugged Pakistan border area where a cell of Germans and Britons at the heart of the U.S. terror alert for Europe _ a plot U.S. officials link to al-Qaida leader Osama bin Laden _ were believed in hiding.

The attack, part of a recent spike in American drone strikes on Pakistan, came as Germany said it has "concrete evidence" that at least 70 Germans have undergone paramilitary training in Pakistan and Afghanistan, and about a third have returned to Germany.

Authorities across Europe have heightened security at airports and other travel hubs as well as at main tourist attractions following the U.S. warning of an al-Qaida-linked terror plot targeting London, Paris, Berlin and other European capitals.

Washington warned Americans over the weekend to use caution when traveling in Europe and imposed a curfew on some U.S. troops based in Germany. On Monday, Britain, Japan and Sweden issued warnings of their own, advising their citizens traveling in Europe to be on alert for possible terrorist attack by al-Qaida or other groups.

Police officers with sniffer dogs patrolled subways in Britain on Monday, while soldiers and mounted police were dispatched to two major churches in Paris _ Notre Dame in the heart of the city and Sacre Coeur on the Right Bank. Paramilitary troops were also seen patrolling the area around the Eiffel Tower _ twice evacuated in recent weeks for unspecified threats.

The U.S. missile strike in Pakistan killed five German militants taking shelter in a house in the town of Mir Ali in North Waziristan, a known hub for foreign militants with links to al-Qaida, Pakistani intelligence officials said.

The terror cell said to be behind the Europe plot _ eight Germans and a Briton _ were believed to have been in hiding in the region. A second Briton was killed in a U.S. strike last month.

A German Foreign Ministry spokesman said Monday that his office was checking the report of the latest killings. He declined to be named in keeping with policy.

However, the German police agency responsible for terrorism investigations, the Federal Criminal Police Office, said as many as 220 people have traveled from Germany to Pakistan and Afghanistan for paramilitary training, and at least 70 have received it. A Pakistani intelligence official last week said there are believed to be around 60 Germans in North Waziristan now.

Despite the growing evidence of a terror plot, France, Britain and Germany _ the nations believed to be the targets of the scheme _ have not changed their terror threat levels. On Monday, the German government played down the fears by declaring there is "no reason to be alarmist."

The threat is being viewed differently by Washington and European capitals, and some analysts said it was a matter of approach. Such differences have played out repeatedly in the years since the 9/11 attacks on the United States, they said.

British intelligence prefers to keep targets under surveillance as they plan attacks, often waiting until the final stages to intervene _ hoping to gather evidence and to gain information about contacts in Britain and overseas.

"That cuts significantly too close to the bone for the United States. They are not happy to let plots run for too long," said Tobias Feakin, director of national security and resilience at London's Royal United Services Institute, a military think tank.

In Germany, the homeland security spokesman for the main opposition Social Democratic party said there is a different security culture in Europe and the United States.

"After 9/11 there were almost daily warnings of new threats in the U.S. which _ thank God! _ never became a reality" in Germany, Dieter Wiefelspuetz said.

In Washington, State Department spokesman P.J. Crowley said Monday that the travel advisory was issued because of extensive evidence of a plot.

"We felt, having tracked intelligence over a lengthy period of time, it was appropriate to issue this alert at this moment," he said.

"We specifically have said continue with your travel plans, but just be cautious because we are aware of active plots against the United States, American citizens and other allies around the world."

German Interior Minister Thomas de Maiziere insisted his nation had no concrete evidence of an imminent attack. "There is no reason to be alarmist at this time," de Maiziere said.

He said he had spoken with U.S. Homeland Security Secretary Janet Napolitano about the travel advisory and that it is not "in keeping with our assessment of the situation."

In a rare public speech last month, MI5 director general Jonathan Evans warned that the risk of attacks can never be completely eradicated.

"We appear increasingly to have imported from the American media the assumption that terrorism is 100 percent preventable and any incident that is not prevented is seen as a culpable government failure. This is a nonsensical way to consider terrorist risk," Evans said.

Many tourists said they planned to be vigilant but would not change their plans.

"I'm very happy to be here in France. I think we're very safe, and I trust the French government to keep us safe," said James O'Connell, 59, of Pittsburgh.

Hannah Haskins, an 18-year-old from Portland, Oregon, who has been in Spain for a month working as an au pair, said she is headed to Britain next week for a visit and will be on guard but not obsessed with the terror alert.

"I probably will be alert and it is going to be high on my mind, but it won't change my plans," she said.

"I will catch the subways, go to the museums and enjoy. There are so many threats and this one is very vague. There is always a threat, so what's the difference?"

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Associated Press writers Asif Shahzad in Islamabad, Paisley Dodds and David Stringer in London, Juergen Baetz in Berlin Shino Yuasa in Tokyo, Eileen Sullivan and Matthew Lee in Washington, Jorge Sainz in Madrid and AP Television News reporter Nicolas Garriga in Paris contributed to this report.