BANGKOK: Thailand’s military launched an airstrike on Cambodian territory on Thursday as a deadly border conflict spiralled out of control, killing at least 12 people—11 of them civilians, including a child. The air assault marks a serious escalation in a long-simmering dispute over their 817-km shared land border.

The Thai army confirmed one of its six deployed F-16 fighter jets fired on a Cambodian military target. “We have used air power against military targets as planned,” said Thai army deputy spokesperson Richa Suksuwanon. Following the strike, Thailand sealed its border with Cambodia.

Cambodia hit back, accusing Thailand of bombing a civilian road and condemned the “reckless and brutal military aggression.” Cambodian officials demanded an immediate withdrawal of Thai forces and warned of further escalation.

Tensions flared after a Thai soldier lost a leg to a landmine Bangkok alleges was newly planted in disputed territory. In response, Thailand expelled Cambodia’s ambassador, recalling its own envoy a day earlier.

Thailand claims Cambodian artillery killed 11 civilians and a soldier in Surin province, injuring 24 civilians and seven troops. Residents in the area fled to bomb shelters. “How many rounds have been fired? It’s countless,” a local woman told TPBS while sheltering.

Cambodia, however, denied responsibility for civilian deaths and called Thailand’s strike “unprovoked.”

Both countries blame each other for triggering the clash. The border has seen sporadic violence over the years, including deadly skirmishes in 2011. This latest round began in May when a Cambodian soldier was killed in a brief shootout.

Malaysia’s Prime Minister Anwar Ibrahim, current ASEAN chair, urged restraint. China also voiced concern and offered to mediate.