Strasbourg — Police fired tear gas and arrested some 100 anti-NATO protestors in Strasbourg Thursday in clashes that broke out as hundreds of masked activists tried to march on the heart of the summit city.

Tensions were running high in the eastern French city hours before a major NATO summit kicks off on Friday, with 25,000 police on stand by to contain huge street protests set draw tens of thousands of people.

Police fired tear gas Thursday as 600 to 2,000 people tried to march from a "peace camp" set up in the south suburbs to the city centre, which is locked down for the high-security two-day event.

Masked protestors clad in black used wooden stakes to smash bus shelters and set fire to trash bins, setting up a barricade before police disbanded the marchers and pushed them back towards their camp.

A German photographer working for the DPP news agency was injured in the clashes, his employer told AFP.

A police spokesman said calm had been restored in the early evening.

But French authorities fear more trouble Friday and Saturday from a hard core of some 2,000 protestors they consider violent and dangerous, in addition to the threat of a terror attack motivated by NATO’s war in Afghanistan.

Paris, which last month announced its return to NATO’s military command after a 40-year absence, has rolled out its biggest security operation since a Group of Eight summit in Evian in 2003 for the summit.

Air space over Strasbourg and its German neighbours Kehl and Baden Baden will be shut down as US President Barack Obama joins 27 leaders for a gathering marking the alliance’s 60th anniversary.

Some 10,000 French police including crack anti-riot squads are being deployed while Germany is positioning 14,600 security forces and, exceptionally, 600 soldiers.

Between 30,000 and 60,000 people, from peaceniks to radical leftists and anarchists, are converging on Strasbourg with the stated aim of disrupting the summit.

Anti-NATO activists will join a mass protest starting in Kehl Saturday, crossing the Europe Bridge to Strasbourg.

Some 3,000 protestors had already checked into the "peace camp" in the south suburbs by Thursday, its tents festooned with anti-military flags and slogans ranging from "War is Terror" to "NATO Game Over."

One activist, who gave his name as Ben, told AFP protest action was planned at five or six strategic locations in Strasbourg.

"Tensions have ratcheted up a notch. There is a risk things could spill over," he said.

Two high-security Orange and Red zones have been set up around the summit venue in Strasbourg and residents have been given special badges allowing them to walk around their neighborhoods.

Clashes broke out Tuesday between police and about 150 activists angry at the intrusive security and stepped-up identity checks, with officers firing tear gas and protesters hurling rocks at police cars.

French Interior Minister Michele Alliot-Marie defended the security clampdown in parliament Thursday, saying it was to protect residents, foreign dignitaries and demonstrators from "extremists who have already made clear, including on the Internet, that they intend to provoke or cause violence."

The summit formally opens in Baden Baden, some 70 kilometres (40 miles) from Strasbourg on Friday evening, with a working dinner at the Kurhaus spa resort hotel.

The 28 leaders then travel to Kehl on Saturday for a group photo before crossing the Rhine to Strasbourg for a meeting of the North Atlantic Council, NATO’s top decision-making body.

AFP/Expatica