The A 45 packs the world's most powerful four-cylinder engine.

Mercedes-Benz has lifted the veil off of the A 45 AMG at the Geneva Motor Show. Designed to take on the Audi S3, the A 45 is the smallest Mercedes ever tuned by AMG.

The A 45 wears an aggressive look thanks to muscular bumpers front and back, a discreet spoiler mounted above the rear window and a slightly lowered ride height. The back bumper incorporates a pair of chromed rectangular exhaust tips, and the front end is fitted with a model-specific two-slat grille. "TURBO AMG" badges affixed to both front fenders add a finishing touch to the car's appearance and boldly inform other motorists that they are not looking at a run-of-the-mill CDI-powered A-Class.

Carbon fiber trim on the dash, red seatbelts and bucket seats upholstered in black leather with red stitching create a performance-inspired environment inside the car. The hot hatch comes standard with a mult-function three-spoke steering wheel and an AMG-specific instrument cluster that incorporates a timer.

Under the hood lies a turbocharged 2.0-liter mill that churns 360 horsepower and 331 lb-ft. of torque, statistics that make it the most powerful mass-produced four-cylinder engine in the world. Hand-built, the engine transmits power to all four wheels via a dual-clutch seven-speed automatic transmission and a brand-new version of Mercedes' 4Matic all-wheel drive system.

The A 45 sprints from zero to 62 mph in 4.6 seconds and its top speed is electronically limited to 155 mph. It is capable of returning up to 34 mpg in a mixed European cycle when driven conservatively.

Mercedes is hoping the dynamic hatchback will help transform the image of the AMG sub-division.

"The A 45 AMG will enable Mercedes' AMG division to appeal to new customers and tap new markets," said Ola Källenius, Chairman of Mercedes-AMG GmbH.

The 2013 A 45 AMG will not be sold in the United States but expect the powerful four-banger to be offered under the hood of the new CLA-Class. An AMG-tuned variant of the upcoming GLA-Class crossover is also believed to be in the works.

Live images by Ronan Glon.