SURIN, Thailand— Thailand and Cambodia traded accusations Saturday of fresh attacks as deadly border clashes entered a third day, leaving at least 33 people dead and more than 168,000 displaced, as international pressure mounted on both sides to reach a ceasefire.

Artillery fire and gunshots were reported near several border villages, expanding the area of the fighting that flared again Thursday after a land mine explosion along the border wounded five Thai soldiers. Cambodian and Thai officials claimed to have acted in retaliation.

Both countries recalled their ambassadors and Thailand closed its northeastern border crossings with Cambodia.

Cambodian authorities reported on Saturday 12 new deaths, bringing its toll to 13, while Thai officials said a soldier was killed, raising the deaths to 20, mostly civilians.

The regional bloc, the Association of Southeast Asian Nations, or ASEAN, is under growing pressure to defuse the situation between its two members. During an emergency meeting on Friday, members of the U.N. Security Council called for de-escalation and urged ASEAN to mediate a peaceful solution.

The 800-kilometer (500-mile) frontier between Thailand and Cambodia has been disputed for decades, but past confrontations have been limited and brief. The current tensions broke out in May when a Cambodian soldier was killed in a confrontation that created a diplomatic rift and roiled Thailand’s domestic politics.

Fresh attacks and rising tension

Cambodia’s Defense Ministry condemned what it said was an expanded Thai offensive early Saturday after five heavy artillery shells were fired into multiple locations in the province of Pursat, calling the attack an “unprovoked and premeditated act of aggression.”

Ministry spokesperson, Lt. Gen. Maly Socheata, said tensions flared in the province of Koh Kong, where four Thai naval vessels were reportedly stationed offshore and four others en route. She said the naval deployment was an “act of aggression” that risked further escalation.

Maly Socheata said seven civilians and five soldiers were killed in two days of fighting. Earlier, one man was reported dead after a pagoda he was hiding under was hit by Thai rockets.

The Thai army had denied targeting Cambodian civilian sites and accused Phnom Penh of using “human shields” by positioning their weapons near residential areas.

Meanwhile, Thailand’s navy, in a statement Saturday, accused Cambodian forces of initiating a new attack in the province of Trat, saying Thai forces responded swiftly and “successfully pushed back the Cambodian incursion at three key points”, warning that “aggression will not be tolerated.”

Thai authorities also alleged several Cambodian artillery shells had landed across the border in Laos, damaging homes and property. Lao officials have not publicly responded to the claim.

The conflict has so far left thousands displaced.

Cambodia’s Information Minister Neth Pheaktra said Saturday the clashes had forced 10,865 Cambodian families, or 37,635 people, in three border provinces to evacuate to safe locations, while Thai officials said more than 131,000 people had fled their border villages.

Call to protect civilians amid claim of cluster bomb use

Human Rights Watch urged the U.N. Security Council and concerned governments to press the Thai and Cambodian governments to abide by international humanitarian law and take all steps to protect civilians. Children have been harmed and Thai authorities have closed at least 852 schools and seven hospitals for safety reasons, the rights group said in a statement Saturday.

Both sides have employed rocket and artillery attacks, and after initially denying Cambodian claims that internationally prohibited cluster munitions were being used, a Thai military spokesperson in a statement Friday said that such weapons could be utilized “when necessary” to target military objectives. HRW condemned the use of cluster munitions in populated areas.

Neither Thailand nor Cambodia is party to the Convention on Cluster Munitions, which bans the use of the weapon and Thai authorities had previously used them during a border dispute with Cambodia in February 2011 that left 20 people dead.

“Neither Thailand nor Cambodia appears to be paying attention to international humanitarian law at great expense to civilians,” John Sifton, Asia advocacy director at Human Rights Watch, said in a statement. “Diplomatic efforts underway need to prioritize protecting civilians and civilian infrastructure.”

Thai officials also acknowledged the use of F-16 jets and drones to launch airstrikes.

UN urges ASEAN bloc to mediate

The U.N. Security Council didn’t issue a resolution on the crisis during its Friday emergency session, but Thai Foreign Minister Maris Sangiampongsa said Saturday all 15 member countries called on both sides to exercise restraint, halt attacks, and resolve the dispute peacefully. They also supported ASEAN’s role in mediating between its two member states, he said.

Malaysian Prime Minister Anwar Ibrahim, whose country is the current ASEAN chair, had earlier said Thailand and Cambodia were open in principle to his ceasefire proposal. Malaysian media said Anwar has tasked the country’s foreign minister to mediate peace talks to halt the fighting.

Maris said Saturday his country agreed in principle to the proposal, but insisted that Cambodia must first show sincerity and cease hostilities, adding that Thailand would continue to engage constructively with Malaysia.

“Thailand reaffirms its commitment to resolving the conflict peacefully and in accordance with international law,” he said, urging Cambodia to “return to the negotiating table with sincerity and in good faith.”