Sniffer dogs can use the collected odours to pick out individuals

The method, once used by East Germany's secret police, the Stasi, involves collecting scent samples in advance from selected targets.

The scents are then passed to police equipped with sniffer dogs who can pick the individuals out amid a crowd.

Past G8 summits have suffered serious unrest, which Germany is keen to avoid.

A state that adopts the methods of the East German Stasi, robs itself of every... legitimacy

Petra Pau, opposition politician

The Interior Minister, Wolfgang Schaeuble, has defended the authorities' decision to use scent tracking, saying it is a useful tool to identify suspects.

A spokesman for the federal prosecutor has confirmed that samples of smell were gathered from five people who were detained during recent police raids.

Odour sample jars are now on display at the Stasi museum

Investigators using sniffer dogs were able to compare the scent samples with traces left at the scene of more than a dozen arson attacks which are believed to be linked to anti-globalisation activists.

The deputy speaker of parliament, Wolfgang Thierse, warned the authorities not to use techniques which could lead to a police state like the former Communist regime.

And Petra Pau, a politician from the opposition Left Party, described the move "as another step away from a democratic state of law toward a preventive security state".

"A state that adopts the methods of the East German Stasi, robs itself of every... legitimacy," she said in a statement.

Keeping tabs

The Ministry for State Security, known as the Stasi, which acted as East Germany's secret police and intelligence agency throughout the Cold War, used odour recognition to keep tabs on potential dissidents.

Germany is keen to avoid the kind of unrest seen at past summits

The samples were then stored in glass jars, each carefully labelled with details of whom the sample came from. Some of the jars are now on display at the Stasi museum in Berlin.

The meeting of leaders of the Group of Eight (G8) most industrialised nations is due to take place from 6-8 June.

As the current holders of the G8 presidency, Germany is playing host to the summit, which is being held in the Baltic Sea resort of Heiligendamm.

Past summits have been targeted by thousands of anti-globalisation activists and protests have often turned violent.