Over the weekend tens of thousands of Turks and a smaller number of Kurds demonstrated in Western Europe.

Some 7,000 Turks from the Netherlands, Belgium and Germany took to the streets in the Dutch city of Utrecht; though windows were smashed, the demonstration remained largely peaceful, and police managed to keep the situation under control.

Yet in Brussels some 100 protesters of Turkish origin were arrested Sunday after an illegal demonstration ended in clashes with Belgian police.

In Berlin, a city home to an estimated 200,000 Turks, a protest against the Kurdistan Workers Party, known by its acronym PKK, on Sunday also turned violent.

The demonstration in Berlin’s immigrant-dominated districts of Kreuzberg and Neukoelln was organized under the slogan “Unity and fraternity between Turks and Kurds,” but that changed when a group of young Turks began to yell extremist chants and throw stones into Kurdish restaurants.

According to the Berliner Zeitung newspaper, the situation escalated when a small group of protesters believed to be members of the extremist Turkish nationalist group Gray Wolves tried to free a man arrested by police. A street battle ensued around Kottbusser Tor, an urban square dotted with Kebab restaurants and Turkish cafes. Demonstrators injured 18 police; 15 protesters were arrested.

This reporter tried to reach the scene of the demonstrations via subway, yet several trains were canceled because subway stations were overcrowded with young Turkish protesters waving Turkey’s flag and chanting anti-PKK, pro-Turkey and pro-Islam slogans.

On Saturday some 500 Kurds demonstrated in Berlin’s posh Charlottenburg district against a Turkish military operation in Iraq, but things remained peaceful.

On Monday German security officials said they expected more violence if the conflict between Turkey and the Kurdish rebels hiding in mountainous northern Iraq continues.

Claudia Schmid, head of Berlin’s Office for the Protection of the Constitution, a domestic intelligence and security agency, said Berlin is home to some 1,000 members of the Kurdish rebel group PKK, branded by the United Nations and the European Union a terror organization.

"The conflict in the border region of Iraq has come to Berlin, and we need to be very careful and keep our eyes open," she told a Berlin-based radio station.

While some criticized police for arriving at the scene too late and in too few numbers, police officials said officers were able to prevent an even larger outbreak of violence. They spoke of Turkish gangs armed with machetes, ready to use them against Kurds.

The violence in Europe demonstrates how tensions are rising in the conflict that started on Oct. 21 when 12 Turkish soldiers were killed in an ambush by PKK fighters, some 3,500 of whom are believed to be hiding in mountainous northern Iraq, right at the border with Turkey.

The public pressure in Turkey to act against the PKK rebels is increasing each day, reflected by massive -- partly violent -- demonstrations in several Turkish cities with hundreds of thousands of participants.

Iraqi and U.S. authorities have not been able to stop the violence originating from northern Iraq; they have also denied Turkish calls to hand over PKK leaders.

Faced with little progress within Iraq, Turkish lawmakers earlier this month gave the formal green light to a Turkish military operation against the rebels. Senior Turkish politicians, however, have said they would not rush into a military mission but would rather lead an operation together with the United States. Experts have also said the PKK is doing everything it can to provoke Turkey into marching across the Iraqi border.

Washington is trying to defuse tensions between some of its staunchest allies in the region: On the one hand NATO member Turkey, which fosters close ties with the United States, and on the other hand the Iraqi Kurds, who after years of oppression after the U.S.-led Iraq war established a self-governed, pro-American, pro-business province in northern Iraq.

U.S. Secretary of State Condoleezza Rice will visit Istanbul on Friday, and President Bush will visit the Turkish capital three days later. The U.S. diplomatic offensive intends to prevent a military one, which all observers agree would have terrible consequences for the entire region.