BANGKOK — Thai and Cambodian troops clashed for a third day on Sunday in the first major territorial encounter since an informal cease-fire that followed four days of fighting in February. At least 10 people were killed and thousands of residents were evacuated from border areas, according to reports from both sides.

The United Nations called on the countries to settle the conflict peacefully, with an effective and verifiable cease-fire. The exact cause of the latest clash, which began early Friday, was unclear, with the two sides accusing each other of making the first move in what was mostly a long-range artillery duel.

The fighting was reported at border areas 100 miles west of Preah Vihear, an 11th-century temple that has been the focus of armed tensions since it was listed in 2008 by the United Nations as a World Heritage site under Cambodian administration.

Both nations claim ownership of a strategic area of 1.8 square miles near Preah Vihear. Two other ancient Hindu temples in the border area are the focus of the latest eruption of fighting.