Gunfire, rockets and bombs dropped by F-16 fighter jets thundered across the long-contested border between Thailand and Cambodia on Thursday, killing at least a dozen people, in a drastic escalation of hostilities between the two neighbors.

The Cambodian and Thai militaries exchanged gunfire in at least six areas in Thailand, according to Thai officials. At least 11 civilians and a soldier were killed and two dozen more people were wounded. Thousands were told to leave their homes near the border.

Thailand responded by sending F-16 jets to strike targets in Cambodia. The Cambodian authorities did not immediately release details about casualties. A group of monks there said they had abandoned their pagoda near the border.

It was the latest deadly conflict to erupt over a decades-old flashpoint between the two countries — one that is rooted in borders drawn by France when it was a colonial power. Thailand and Cambodia each claim ownership of Prasat Ta Muen Thom, an ancient temple perched on the forested Dangrek mountains that divide the two countries.

The event that prompted the current violence appears to have been a land mine explosion near the temple on Wednesday, in which a Thai soldier lost a leg. Thailand accused Cambodia of laying mines in Thai territory, while Cambodia accused Thai troops of venturing into its territory. The episode followed months of simmering tensions and a fatal skirmish in May that killed a Cambodian soldier.