BANGKOK — An eruption of violence in the southern Philippines and suicide bombings in Indonesia this week highlight the growing threat posed by militant backers of the Islamic State in Southeast Asia.

While the timing of the Jakarta bombings and the fighting on the southern Philippine island of Mindanao appears to be coincidental, experts on terrorism have been warning for months that the Islamic State, also known as ISIS, has provided a new basis for cooperation among extremists in the region.

“Setbacks in Syria and Iraq have heightened the importance of other theaters for ISIS, and in Southeast Asia, the focus is the Philippines,” said Sidney Jones, director of the Institute for Policy Analysis of Conflict, based in Jakarta. “ISIS supporters around the region have been urged to join the jihad in the Philippines if they can’t get to Syria, and to wage war at home if they can’t travel at all.”

There is no indication that this week’s violence was directed or coordinated by Islamic State leaders in the Middle East. Still, the attacks posed a test for the authorities in the Philippines and in Indonesia, the world’s largest Muslim-majority nation, as they confront like-minded extremists who support the creation of an Islamic state in Southeast Asia.