Greek authorities are on alert after anti-terror units discovered evidence of a bungled rocket attack against the headquarters of Mercedes Benz, hours after a guerilla organisation claimed responsibility for a previous assault against the German ambassador's residence in Athens.

Fuelling further fears of a resurgence of violence in a country torn by political unrest, extremists calling themselves "group of popular fighters" declared they were at war with "the German capitalist machine".

The group said it had attacked the Athens branch of Mercedes-Benz, firing a rocket into its central offices on the northern fringes of the capital on 12 January.

Following up on the claims, last night, experts discovered ground markings that suggested a rocket had indeed been fired in the vicinity of the outlet but, missing its target, had landed in a field.

One source, who spoke on condition of anonymity, described it as a "blind attack" capable of causing great bloodshed had it hit homes in a residential area nearby.

In a 12,000-word proclamation, sent to Pontiki, a satirical magazine, the organisation claimed the previous attack on the ambassador's home had been spurred by the corrosive effects of austerity.

"As we sprayed gunfire at the hyper-luxury home of the German ambassador we imagined beside us the thousands of people who line up at soup kitchens … the unemployed, those working for €400 [a month]," the group said.

They said they had carried out that attack to avenge the memory of Dimitris Christoulas, a pensioner whose public suicide in Athens' main Syntagma Square in April 2012, sent tremors through the nation.

Like many Greeks who have taken their own lives, Christoulas left a note saying the financial crisis was too much to bear.

Greece has become increasingly polarised between far left and far right in the wake of the financial crisis.