Thailand and Cambodia sent troops and heavy guns today to their disputed border, where hundreds of soldiers faced off for a fifth day over an ancient Hindu temple.
Despite the military build-up, both sides said they were ready to negotiate an end to the stand-off.
The dispute has raised investor fears of a major confrontation. Thailand's main stock index has fallen more than 23 percent since anti-government street protests in Bangkok began in late May, and could drop further if border tensions get worse, analysts said.
The Preah Vihear temple, perched on a jungle-clad escarpment that forms a natural boundary, has been a source of tension since the International Court of Justice ruled in 1962 it belonged to Cambodia, a decision that still rankles Thais.
The listing of Preah Vihear as a World Heritage site this month triggered a political uproar in Thailand, stoked by groups opposed to Prime Minister Samak Sundaravej whom they accuse of being a proxy of former Prime Minister Thaksin Shinawatra, who was ousted in a 2006 coup.
The diplomatic sparring between Bangkok and Phnom Penh has intensified ahead of high-level talks on Monday involving the two countries' defence ministers.
Thailand summoned Cambodia's ambassador yesterday to respond to Prime Minister Hun Sen's charge that Thai troops had "encroached" on Cambodian territory" and that the situation was "worsening".
In a letter to Hun Sen, Samak said Cambodian troops and buildings on the disputed 4.6 sq km (1.8 sq mile) area were a "violation of Thailand's sovereignty and territorial integrity".
He added his government was "resolved to seek a just and peaceful solution to the situation".
Cambodia has asked the United Nations' Security Council to discuss the border dispute with Thailand, a Thai government spokesman said.
"We have been informed by our ambassador to the UN that Cambodia has filed a complaint over the dispute to the UN," he said.