 On 29 November, Roosevelt asked Stalin five questions about data and intelligence relating to Japanese and Siberian ports, and about air bases in the Maritime Provinces for up to 1,000 heavy bombers.On 2 February, Stalin told the American ambassador that America could operate 1,000 bombers from Siberia after the Soviet Union had declared war on Japan (Vladivostok is in the Russian Far East, not Siberia).According to Soviet reports, German agents planned to kill the Big Three leaders at the Tehran Conference, but called off the assassination while it was still in the planning stage.