American travellers, including US government employees, were discouraged from travelling to Mindanao in the Philippines amid security threat which came on the eve of US Secretary of State John Kerry\'s two-day visit to Manila, the Philippines News Agency (PNA) said, citing US Embassy notice issued Thursday. The US has detected additional security threats in Southern Mindanao as certain individuals associated with known extremist or insurgent groups may be planning attacks in several areas, the US embassy notice said. \"The US Embassy wishes to alert US citizens that a series of credible security threats have been identified in southern Mindanao,\" it said in an emergency message for US citizens that was posted on the embassy\'s website today, the PNA report said. \"The embassy is aware of threats in several locales in Region 11 (the Davao Region), Region 12 (North and South Cotabato, Sultan Kudarat, and Sarangani), and in Maguindanao. Individuals associated with known extremists and insurgent groups are believed to have been conducting surveillance on a number of public locations in these areas, as possible targets of interest,\" the advisory said. \"The embassy strongly reiterates its recommendation that US citizens exercise extreme caution when travelling to Mindanao and keep personal safety and security in mind during any stay in Mindanao,\" the notice said. An estimated 400,000 American citizens, which would include naturalized citizens of Filipino origin, are living and working in the Philippines, the PNA report added.