The U.S. State Department has reissued a travel warning for the Philippines, citing terrorism and kidnapping concerns in the southern part of the 7,000-island nation.

The warning, issued Tuesday and replacing a warning issued in April, urges travelers to avoid “all non-essential travel to the Sulu Archipelago and through the southern Sulu Sea.”

Travelers should “exercise extreme caution,” it notes, when traveling to Mindanao, the second-largest island in the country. Only Luzon to the north, home to Manila, the capital, is larger.

Earlier this month, three Philippines soldiers were killed when they clashed with Abu Sayyaf rebels in Sulu, the Mindanao Examiner reported

Abu Sayyaf is an Islamist extremist group whose origins date to the 1990s. Mindanao and the southern Philippines have a large Muslim population, which has been at odds with the Christian north almost since the Spanish began to colonize the islands in the 1500s.

The State Department warning notes, “Separatist and terrorist groups continue to carry out attacks and kidnappings against civilians, foreigners, political leaders and Philippine security forces in Mindanao.

”Since January 2016, at least 13 separate kidnappings of foreigners have been reported across Mindanao.“

Davao City, with about 1.5-million residents, was hit by a terrorist bombing in September that killed at least 14 and injured more than 65, CNN Philippines reported.

”Following the attack,“ the warning notes, ”the Philippine government declared a ‘State of National Emergency on Account of Lawless Violence in Mindanao.’“

The warning notes that no Americans have been targeted, but U.S. foreigners often are threatened.