Schäuble said in a series of press interviews that potential troublemakers could be detained for up to two weeks if there were firm indications they are planning criminal actions.

"Regional police authorities are considering taking recourse to so-called preventative detention," Schäuble told Germany's top-selling newspaper, Bild.

In Germany, people can be put behind bars for 14 days if police find evidence that they are planning a crime. The government had threatened to do this with hooligans during the soccer World Cup in Germany last summer.

The minister has already announced that Germany was re-imposing border checks in efforts to quell violent protests at the June 6-8 summit in the Baltic Sea resort of Heiligendamm.

Reintroduction of border checks

Normally German borders are open and passengers on flights from many European Union countries, the so-called Schengen nations, do not need to show passports. The Interior Ministry said it needed to stop potential offenders, mainly opponents of globalization, from entering Germany to protest at the summit.

Schäuble said Germany expected an increased security threat during the summit. He said the fact that Germany was not subject to terrorist attacks during major events such as last year's World Cup "does not mean we will be spared this time."

Berlin is expecting up to 100,000 protestors to target the G8 summit in the Baltic Sea resort. Authorities are planning to deploy 16,000 police in Heiligendamm and the nearby city of Rostock

The authorities are building a 12-kilometer-long (7.5-mile-long) security fence to protect the leaders attending the event.

Police raids prompt anger

On Wednesday, police launched a crackdown against left-wing extremists they believed were intent on disrupting the talks between leaders from Germany, Britain, Canada, France, Italy, Japan, the United States and Russia.

The authorities searched 40 sites throughout northern Germany linked to 18 suspects thought to belong to a far-left group that was preparing arson attacks and other violent protests against the summit.

The prosecutor's office in the south-western city of Karlsruhe said nearly 900 police officers had taken part in the raids, which also targeted three suspects believed to belong to a radical group known as "Militante Gruppe" (mg) that is suspected of being behind 25 attacks since 2001.

"The suspects linked to the militant, left-wing extremist scene are accused of founding or belonging to a terrorist organization whose aim is to disrupt or prevent the upcoming G8 world economic summit taking place in early summer 2007," the office said in a statement.

Crackdown mobilizes left-wing protestors

Anti-globalization group Attac slammed the raids as "an attempt to criminalize the entire spectrum of G8 opponents." The group claims that the police offensive has been counterproductive in terms of security and says even more activists are expected in cities such as Rostock, near the G8 summit location of Heiligendamm.

"One of the consequences of the police operations was to mobilize people," Peter Wahl from Attac told ZDF television Friday. "We have received a lot of e-mails from people saying 'at first I did not want to go to Rostock ... but now I am ready,'" he added.

Fears about security were raised when opponents of the summit claimed responsibility for torching a car on the property of a German finance ministry official in the northern city of Hamburg in December.

Protesters have also splashed paint on the summit hotel.

Several G8 summits in recent years have been scarred by violence, most notably the meeting in the Italian city of Genoa in 2001 when an anti-capitalist protester was killed by police during riots.

Demonstrations at recent G8 summits have been kept well away from the venue, although violence has broken out in nearby towns.