MANILA - Citing "continued terrorist threats, insurgent activities, and kidnappings," the United States on Tuesday urged its citizens anew to avoid all non-essential travel to Sulu province and "exercise extreme caution" when traveling to Mindanao.

"Separatist and terrorist groups continue to carry out attacks and kidnappings against civilians, foreigners, political leaders, and Philippine security forces in Mindanao," the US State Department said in its its newly-updated travel warning.

"There have been no reports of U.S. citizens in Mindanao targeted specifically for their nationality; however, general threats to U.S. citizens and other foreigners throughout Mindanao remain a concern."

The US State Department cited the 13 separate kidnappings of foreigners reported across Mindanao since January, and the September 2 bombing of Davao City which killed at least 15 people and prompted the declaration of a state of national emergency.

The travel alert, which replaced a warning released last April, covers areas from the southern tip of Palawan, along the coast of Sabah, Malaysia and Sulu, and up to Zamboanga City.

US Embassy employees were also instructed to secure special authorization from higher security officials to travel to any location in Mindanao.