Berlin ? President Bush told skeptical allies “we’ve got to be tough” on terrorism Wednesday as thousands of anti-war protesters greeted his arrival in Europe and German leaders questioned U.S. hopes of toppling Saddam Hussein.

Opening a seven-day, four-nation trip, Bush warned that Europe may be terrorists’ next target.

Protesters carry posters reading War

“Even though we’ve had some initial successes, there’s still danger for countries which embrace freedom, countries such as ours, or Germany, France, Russia or Italy,” the president said as he left the White House shortly after dawn.

Seven hours later, Bush stepped off Air Force One onto a red carpet lined by white-jacketed military troops. For his only appointment, Bush ducked into a coffee house at the site of the old Berlin Wall with German Chancellor Gerhard Schroeder, U.S. Ambassador Dan Coats and Berlin Mayor Klaus Wowereit.

Schroeder has tried to position himself as a staunch anti-terrorism ally without embracing tough action against Iraq. In a German TV interview, he said Iraq was a threat, “and that’s why we are together exerting pressure so that Saddam Hussein lets international observers into the country.”

Bush wants a stronger commitment from Germany and other U.S. allies.

“As an alliance, we must continue to fight against global terror,” he said before leaving Washington. “We’ve got to be tough.”

The blunt words, aimed for consumption at home as well as in Europe, dovetailed with the administration’s effort in recent days to prepare Americans for the inevitability of another attack.

Those warnings have been in part a response to Democratic suggestions that the administration missed warning signs before the Sept. 11 attacks, U.S. officials have said.

Bush is trying to build a case for widening the war beyond Afghanistan to other terrorist hot spots, primarily Iraq. Secretary of State Colin Powell said Bush wouldn’t shy from that policy in talks with Schroeder.

Protests by some 20,000 anti-war demonstrators were generally peaceful, but violence broke out among groups of hooded youths and pro-Palestinian demonstrators. An American flag was burned, and demonstrators pelted police in riot gear with bottles and stones.

With 10,000 officers, the largest police operation since World War II, officials blocked off several streets around the downtown hotel where Bush was staying. The hotel is just east of the Brandenburg Gate, the symbolic dividing line between the old communist regime and the West.

A huge portrait of the White House hung from the landmark.

Bush intended to spend barely 20 hours in the German capital before flying today to Moscow, where he will sign a landmark agreement with Russian President Vladimir Putin to reduce each nation’s nuclear arsenals.