MILAN (Reuters) - A sonic boom rippled across northern Italy on Thursday after the air force scrambled two fighter jets to intercept a French passenger plane that temporarily lost contact with ground control.

Terrified residents called emergency services in the region of Lombardy, around the financial capital Milan, and the Alpine region of Val d’Aosta. Some schools and a court house were evacuated as a precaution in the city of Bergamo.

The source of the alert was a Boeing 777 operated by Air France, which lost contact with Italy’s air traffic agency as it flew over the country’s industrial heartland.

Two Eurofighter F-2000 jets intercepted the plane and “made sure the crew restored contact with air traffic authorities”, the air force said in a statement. It did not say why radio contact had been broken off.

“Given the urgency of the situation, the two military aircraft broke the sound barrier to reduce the response time to a minimum,” the statement said.

“The wind and temperature amplified the spread of the shockwave, making it particularly audible on the ground.”