MANILA - The United States told its citizens to avoid all "non-essential travel" to several areas in the southern region of the Philippines.
In a travel warning issued on Monday, the US warned its citizens against travelling to Marawi City, to the region of Mindanao and to the Sulu Archipelago including the Sulu Sea due to "terrorist threats, insurgent activities, and kidnappings."
"There is a threat of kidnappings-for-ransom of foreigners, including US citizens, from terrorist and insurgent groups based in the Sulu Archipelago and in the southern Sulu Sea area," the travel warning from the US State Department read.
"This area stretches from the southern tip of Palawan, along the coast of eastern Sabah, Malaysia and the islands of the Sulu Archipelago, up to Zamboanga City, Mindanao."
"Separatist and terrorist groups continue to attack and kidnap civilians, foreigners, political leaders, and Philippine security forces in Mindanao," it added.
The US Embassy also required US government personnel to obtain "special authorization" before traveling to Mindanao and the Sulu Archipelago.
The Embassy also reminded its citizens of the recent attacks supposedly perpetrated by extremists in the southern region, such as the September 2016 Davao City bombing, which killed 14 and injured at least 70.
It also noted of the ongoing Marawi crisis, which erupted when government forces in May tried to capture extremist leader Isnilon Hapilon.
Martial law is currently in place over the entire Mindanao islands because of the violence, which has so far killed more than 500 people.
President Rodrigo Duterte's martial law declaration is set to expire this week, and he has called the members of Congress to convene on its extension.