Long-festering tensions over border territory have escalated into armed conflict between Cambodia and Thailand, leading to dozens of deaths on both sides and displacing tens of thousands of people.

The Southeast Asian neighbors, who share a disputed 500-mile frontier, have long fought over the sovereignty of a 1,000-year-old temple.

BANGKOK -- Armed clashes have broken out between Thailand and Cambodia in long-disputed border areas, rapidly escalating months-long tensions.

For more than a century, Thailand and Cambodia have laid claim to undisputed points along their 817-km (508-mile) land border. This has led to skirmishes over several years and at least a dozen deaths, including during a weeklong exchange of artillery in 2011.

Thailand has one of the best-equipped and trained air forces in Southeast Asia, with an estimated 46,000 personnel, 112 combat-capable aircraft, including 28 F-16s and 11 Swedish Gripen fighter jets, and dozens of helicopters.

Thailand favours bilateral negotiation rather than third-party mediation to resolve its military conflict with Cambodia, two Thai officials said, as fighting along their disputed border continued unabated.

"The U.S. already flunked the test and that should be a wakeup call," a former senior U.S. State Department official told Newsweek.