Greek police said Friday they are investigating a threat to the country's central bank governor Yorgos Provopoulos after an envelope containing two bullets was sent to his office. Politicians, state officials, police officers and representatives of the business world have been often targeted by anarchist guerilla groups in Greece for years and attacks have spiked amidst the debt crisis. Earlier this week arsonists targeted the political office of Interior Minister Yannis Michelakis in central Athens, causing minor material damage. Last year Finance Minister Yannis Stournaras received a similar envelope with a bullet. Authorities are on alert after the recent escape of a convicted terrorist during a leave of absence from prison during the holiday season, fearing more serious attacks. In December a group of armed assailants fired with automatic rifles against the German ambassador's residence in Athens, causing only material damage.