Thai and Cambodian troops exchanged artillery fire on Sunday in a third day of fighting that has killed 10 soldiers and uprooted thousands of villagers from their homes.

Officials from both sides said the clashes over disputed territory lasted about two hours on Sunday morning. Cambodian military officials said the shooting resumed in the afternoon.

U.N. chief Ban Ki-moon called for a ceasefire, but the prospects for peace appeared shaky, with the two sides disagreeing on what triggered the fighting and differing on how to negotiate the conflicting territorial claims underlying the crisis.

Thailand reported no new casualties, after four of its soldiers were killed and 17 wounded over the previous two days. Witnesses saw one Cambodian soldier and a Cambodian television journalist wounded on Sunday. Colleagues said the journalist suffered a head wound but did not appear seriously hurt. Cambodia earlier reported the deaths of six soldiers.

The dispute between the neighbours stems from their claims over small swaths of land along the border, with nationalistic politics fuelling tensions. Clashes have erupted several times since 2008, when Cambodia’s 11{+t}{+h} century Preah Vihear temple was given U.N. World Heritage status over Thai objections.

The current round of clashes is the first reported since February, when eight soldiers and civilians were killed near the Preah Vihear temple. The latest fighting is about 160 km west of there.

Mr. Ban has called on Cambodia and Thailand to implement an effective and verifiable ceasefire. A U.N. statement late Saturday said Mr. Ban believes the dispute cannot be resolved by military means, so the two countries must engage in a serious dialogue to resolve the underlying problems.

Indonesia, a fellow member of the Association of Southeast Asian Nations, has tried to mediate, but its efforts have been stymied so far by Thailand’s reluctance to allow Indonesian military observers in the area of dispute. Thailand insists the problem should be solved through bilateral talks with Cambodia, but Cambodia wants third-party mediation.

On Saturday, Thai Foreign Minister Kasit Piromya said his government is willing to accept Indonesia’s assistance in solving the crisis, but he was awaiting approval from Thailand’s Defence Ministry.

Sunday’s flare-up came after it seemed that calm might have been restored. Witnesses on the Cambodian side said an important border crossing that had been closed for two days had been reopened, and Thai media said some of an estimated 20,000 civilians who had been evacuated from the battle zone were starting to move back. The border crossing, which is not in the battle zone, was shut again shortly after fighting resumed.

Each side has accused the other of starting the latest fighting, which has mainly involved artillery duels at long range.

Thailand rejected accusations Saturday that it had used chemical weapons against Cambodian troops.

A Cambodian Defence Ministry statement charged that Thailand had fired 75- and 105-millimeter shells “loaded with poisonous gas” into Cambodian territory, but did not elaborate. Col. Suos Sothea, a Cambodian field commander, said separately that Thailand had used both cluster shells — anti-personnel weapons banned by many countries — and artillery shells that gave off a debilitating gas.

Mr. Kasit said the allegations were not true, and Col. Tawatchai Samutsakorn, commander of Thailand’s 2nd Army Region, denied that cluster bombs or poison gas had been employed by his forces.

Cluster munitions contain dozens or hundreds of small bomblets that scatter over vast areas. Some can lie dormant for decades until disturbed, posing enormous danger to civilians.

Thailand acknowledged using cluster-type munitions in border fighting in February, but argued that they were not of the type banned from use by 108 countries under an international treaty. Thailand has not signed the pact, but has publicly pledged not to use such weapons.

The fighting comes as Thailand’s military raises its profile in domestic politics ahead of general elections expected by early July. The Army previously effectively vetoed a plan to station Indonesian observers to monitor the border situation.

More In: International | News