JAKARTA, Indonesia — Residents along Indonesia’s Sunda Strait coast were warned on Monday to avoid beaches for at least two days for fear that volcanic activity could generate another powerful tsunami.

Experts were still uncertain what caused the 10-foot-high tsunami on Saturday that killed at least 429 people and injured more than 1,480 on the nearby islands of Java and Sumatra. More than 16,000 people have been displaced and at least 154 are missing.

But evidence was mounting that the deadly wave resulted when volcanic activity on the island of Anak Krakatau set off a landslide on the island’s steep southwest slope.