The United States and Britain issued an advisory for their citizens Thursday warning them to stay away from a southern Philippine region due to a high threat of kidnapping of international travelers. Security concerns in the Sulu archipelago increased after the abduction of 18 Indonesian and Malaysian tug boat crewmen by suspected Muslim extremists in recent weeks.

The U.S. State Department warned Americans to defer non-essential travel to the Sulu archipelago "due to the high threat of kidnapping of international travelers, increased threat of maritime kidnappings against small boats ... and violence linked to insurgency and terrorism there," the Associated Press (AP) reported.

On Wednesday, the British government also issued a similar travel warning, citing "a high threat from terrorism, including kidnapping."

Abu Sayyaf group, which is known for extortion, kidnappings, beheadings and bombings, has been suspected of seizing Indonesian and Malaysian crewmen at gunpoint in separate attacks on three tugboats.

Amid growing concerns, Malaysia, Indonesia and the Philippines plan to conduct a meeting of maritime officials to discuss ways to boost security along their sea borders, the AP reported. Authorities plan to work on ways to use satellite technology to spot suspicious vessels.

The Sunni militant group was established in the early 1990s in Basilan province, about 100 miles northeast of Sulu, and currently has about 400 armed fighters split into several factions.

Last week, the Islamic State group, also known as ISIS, had claimed responsibility for the killing of 100 soldiers in recent clashes between Abu Sayyaf and Philippine troops on the island of Basilan. However, the Philippine government rejected the claims, saying there was no evidence to prove ISIS' links to the local Abu Sayyaf.

Concerns over the spread of ISIS in Southeast Asia have increased as nearly 1,200 people from the region have reportedly joined the extremist group in the Middle East. Several experts have said that an ISIS stronghold in southern Philippines could target the region.