Bangkok, Thailand (CNN) -- Renewed clashes in a disputed area along the Thai-Cambodian border killed at least one Thai soldier and left 11 people injured Saturday, Thailand's MCOT news agency reported.
The skirmish came a day after officials said three Thai soldiers and three Cambodian soldiers were killed in fighting there.
Each side blames the other for the violence, which erupted Friday near two temples in the Phanom Dong Rak district of Thailand's Surin province.
Authorities have evacuated thousands of people from nearby villages.
The Cambodian defense ministry on Saturday blasted what it called Thailand's "repeated deliberate acts of aggression," including firing heavy artillery weapons and flying military planes deep into Cambodian airspace.
In a letter to the U.N. Security Council on Friday, Cambodia's deputy prime minister said Thai troops had engaged in a "large-scale attack with many types of weapons," targeting areas around temples "deep inside Cambodian territory."
Hor Namhong wrote that Thai artillery pieces fell as far as 21 kilometers (13 miles) in its territory during what he called the fifth such attack since 2008 when the U.N. Educational, Scientific and Cultural Organization placed Cambodia's Preah Vihear Temple on its World Heritage List.
Thai Foreign Minister Kasit Piromya, meanwhile, said he'd send off a "protest letter" of his own, the state-run MCOT news agency reported Saturday. He disputed reports that Thai forces had used poisonous gas or flown over Cambodian territory, except for helicopters trying to airlift out wounded soldiers.
"We protected our sovereignty, and our counterattack targeted the Cambodian army base to limit the area of the clash," said Kasit, who added that Thailand still wanted to settle the issues diplomatically.
Thai Deputy Prime Minister Suthep Thaugsuban told MCOT on Saturday that one recent clash began after Cambodian troops fired into Thai territory.Earlier, Thai army Lt. Col. Siriya Khuangsirikul accused Cambodia of violating an agreement not to bring weapons or post troops in the disputed area.
Cambodian Lt. Gen. Chhum Socheat claimed Thai troops shelled and damaged temples, and flew over Cambodian territory with spy planes, Cambodia's state-run Agence Kampuchea Presse reported.
At least 10 people were killed when renewed fighting flared up in another disputed border area between the two nations in February, prompting the U.N. Security Council to issue a statement calling on both sides to implement a permanent cease-fire and "resolve the situation peacefully and through effective dialogue."
The office of Secretary-General Ban Ki-moon said in a statement Saturday that the U.N. chief was "troubled" by the recent clashes, especially after "initial signs of progress" toward resolving their conflict peacefully.
"The Secretary-General calls on both sides to exercise maximum restraint and to take immediate measures to put in place for an effective and verifiable ceasefire," the statement said.
Those clashes, which lasted four days, stemmed from a longstanding conflict related to the 11th-century Preah Vihear temple. Both Cambodia and Thailand lay claim to the temple, which sits atop a cliff on Cambodian soil but has its most accessible entrance on the Thai side.
At the time, each nation accused the other of firing first, according to a statement from the Association of Southeast Asian Nations.
Conflict over the site has taken place periodically for years. In 1962, the International Court of Justice in The Hague, Netherlands, ruled that the site was in Cambodia, adding that the structure was "an outstanding masterpiece of Khmer architecture."
But Thailand says the 1.8-square-mile (4.7-square-kilometer) area around Preah Vihear was never fully demarcated, and blames a map drawn at the beginning of the 20th century during the French occupation of Cambodia.
Thaugsuban said Saturday that the border dispute must be resolved peacefully between the two parties, without the involvement of a third party.
In his latest letter to the United Nations, his Cambodian counterpart Namhong accused Thailand of not being earnest in its bids to resolve the dispute peacefully, calling its neighbor's actions "a pretext for using its larger and materially more sophisticated armed forces against Cambodia."
CNN's Kocha Olarn contributed to this report.