(Recasts with Thai reinforcement, changes dateline)
By Sukree Sukplang
KANTARALAK, Thailand, July 16 (Reuters) - Thailand sent extra troops to its disputed border with Cambodia on Wednesday, an army official said on the second day of a flare-up over a disputed temple.
Thai Supreme Commander Boonsrang Niumpradit said earlier Thai and Cambodian officials were negotiating to end the impasse, which was triggered by Thai protests at the listing of the 900-year-old Preah Vihear temple as a World Heritage site.
But while talks continued, a senior army official said more troops would be sent to the border area, which has been a source of tension between the southeast Asian nations for decades.
"If the Cambodians can send their people to the disputed area, we can send our troops to that area too," the official, who declined to the named, said.
They included soldiers from artillery and special forces units, he said, without giving further details.
At the temple, 140 Thai soldiers and 380 Cambodian troops faced off a day after three Thai protesters were held for several hours after trying to plant a Thai flag on the site.
Cambodian officials say Thai troops are occupying a patch of land on the border that belongs to Phnom Penh. The Thais deny this, and have accused the Cambodians of allowing illegal settlements on disputed territory.
Nevertheless, both sides have said they are seeking to negotiate an end to the stand-off.
"Please be calm and patient. We are talking with the senior people in Cambodia and we hope the situation will ease up in a few days," Boonsrang said.
In Phnom Penh, government spokesman Khieu Khanarith said the Thais should withdraw to their old positions. He also said Prime Minister Hun Sen had appealed for calm and urged the media not to inflame the issue.
On the Thai side of the border, activists planned to rally on Thursday "to protect our sovereignty," a protest leader said.
The only casualty so far has been a Thai paramilitary ranger who lost part of his leg on Tuesday after stepping on a landmine in an area littered with the devices after decades of war.
Perched on top of a jungle-clad escarpment that forms a natural boundary between Cambodia and Thailand, Preah Vihear was off-limits for much of the 1970s to 1990s when it was a jungle outpost for Pol Pot's Khmer Rouge guerrillas.
Built by Khmer kings in the 11th century, it has been a source of tension since the International Court of Justice ruled in 1962 that the Hindu temple belonged to Cambodia, a decision that still rankles Thais.
Thailand's initial support for the temple's heritage listing has been used by anti-government groups to stoke nationalist fervour and protests against the government in Bangkok.
The People's Alliance for Democracy (PAD), a coalition of royalists, activists and businessmen which has led a nearly two-month campaign against the government, called a rally for Thursday on the Thai side of the border.
"We want to tell the Cambodian government to withdraw trespassers on Thai territory or we will exercise our rights under the constitution to protect our sovereignty," PAD leader Veera Somkwamkit told Reuters.
Groups opposed to former Prime Minister Thaksin Shinawatra, who was ousted in a 2006 coup, have accused the new pro-Thaksin government of selling out Thailand's heritage to help his business interests in Cambodia.
Phnom Penh and Thaksin have denied the charge. (Additional reporting by Nopporn Wong-Anan in Bangkok, Ek Madra in Phnom Penh; Writing by Darren Schuettler; Editing by Jon Boyle)