Thai villagers began trickling back to their homes near a disputed stretch of the border with Cambodia on Thursday in a sign of easing tension after deadly clashes over an ancient temple.
But both Thai and Cambodian forces remained on alert a day after Cambodian Prime Minister Hun Sen said the four days of fighting that began last Friday constituted "war".
Both sides have promised maximum restraint and deny beefing-up their forces, but witnesses on the Thai side saw tanks, armoured vehicles and fighter jets on the move.
Thailand and Cambodia blame each other for the clashes near the 900-year-old Preah Vihear temple that killed at least three Thais and eight Cambodians. At least 34 Thais and 55 Cambodians were wounded, according to statements from both sides.
The temple ruins, perched on a cliff overlooking the north Cambodian plain, have been a thorn in the side of relations between the neighbours since the 1950s.
The issue has blown up in recent years partly because of bitter divisions in domestic Thai politics with a pro-establishment "yellow shirt" activist movement whipping up nationalist feelings.
The governor of Thailand's Si Sa Ket province, Somsak Suvarnsujarit, said several thousand villagers had left temporary shelters and returned home.
"Many of those who come from villages further from the fighting range opted to go back," Somsak said, adding that in all, about 21,000 villagers had left their homes.
"Those in the villages right next to the scene of fighting were asked to stay back until it is really safe. For now, the situation remains uncertain and we have not got the all clear from the army."
In Cambodia's northern frontier areas, schools and temples have been turned into shelters for several thousand displaced people.
The Cambodian and Thai foreign ministers are heading to New York where they are due to present their cases to the U.N. Security Council on Monday.
Though the guns have been silent for three days and attention is turning to diplomatic efforts to restore calm, more forces have been heading to the area and witnesses spotted two Thai F-16 fighter jets flying within 10 km (6.2 miles) of Preah Vihear, for about 30 minutes.
The Thai air force said it was a routine exercise.
"We are not flexing muscles or provoking anyone," a spokesman said. "It was a regular air patrol."