Ferrari's Michael Schumacher, aiming for a fourth successive pole position, set the fastest time in Saturday's free practice for the San Marino Grand Prix.

Briton Jenson Button, quickest on Friday afternoon for BAR, again looked a threat with the second best lap in both 45 minute sessions.

Six times world champion Schumacher, winner four times in the last five years at Imola and unbeaten in three races so far this season, lapped the Enzo and Dino Ferrari circuit in one minute 20.125 seconds.

That compared with Schumacher's best time on Friday of 1:20.084 and his 2003 pole position of 1:22.327.

Button's best lap on a warm and sunny morning was 1:20.150, with Spaniard Fernando Alonso and Briton David Coulthard clocking the same time of 1:20.844 for Renault and McLaren respectively.

Schumacher's Brazilian team mate Rubens Barrichello, third fastest in the opening session in 1:21.583, was sixth on the timsheets in the second stint.

Button, third in the championship behind the Ferrari duo, will be chasing his third podium in a row on Sunday after finishing third in Malaysia and Bahrain.

Williams stepped up their preparations for what could be the last grand prix at Imola, on the 10th anniversary of the death of Brazilian champion Ayrton Senna, with the fourth and fifth fastest times in the opening session.

Austrian rookie Christian Klien made a bad start to the day when he crashed his Jaguar early in the first session, skidding off and clouting the tyre wall. The impact broke the car's front right suspension.