By JINTAMAS SAKSORNCHAI

BANGKOK (AP) — Thailand closed northeastern border crossings with Cambodia and said Wednesday it was withdrawing its ambassador and expelling the Cambodian ambassador to protest a land mine blast in which a Thai soldier lost a leg.

Cambodia responded Thursday that it was downgrading diplomatic relations with Thailand to their lowest level and recalling all Cambodian staff from its embassy in Bangkok.

Relations between the Southeast Asian neighbors have deteriorated sharply since May when a Cambodian soldier was killed in an armed confrontation in one of several small patches of land both countries claim as their own territory.

Nationalist passions on both sides have further inflamed the situation, and Thailand’s prime minister was suspended from office on July 1 to be investigated for possible ethics violations over her handling of the border dispute.

The Thai army said the land mine that wounded five soldiers Wednesday had been placed in Thailand’s Ubon Ratchathani province. Cambodia said the blast happened in its Preah Vihear province. A week earlier, a land mine in a different contested area exploded and wounded three Thai soldiers when one of them stepped on it and lost a foot.

Thai authorities have alleged the mines were newly laid along paths that by mutual agreement were supposed to be safe. They said the mines were Russian-made and not of a type employed by Thailand’s military.

The army statement called on Cambodia “to take responsibility for this incident, which constitutes a serious threat to peace and stability in the border region between the two countries.” After last week’s blast, Thailand accused Cambodia of violating the Ottawa Treaty, an international pact that bans the production and use of anti-personnel land mines.

Cambodia rejected Thailand’s account as “baseless accusations.”

Defense Ministry spokesperson Lt. Gen. Maly Socheata said the land mine explosion took place on Cambodian territory and alleged Thailand had violated a 2000 agreement “regarding the use of agreed paths for patrols.”

Cambodia has denied that it laid new mines along the border, pointing out that many unexploded mines and other ordnance are a legacy of 20th century wars and unrest.

Thailand’s acting Prime Minister Phumtham Wechayachai said the Foreign Ministry would make an official protest to Cambodia, and further measures would be considered.

Cambodia’s Foreign Ministry said in a statement Thursday that it demanded all Thai diplomatic staff leave Cambodia and was recalling Cambodia staffers at the embassy in Bangkok.

Many border checkpoints had already been closed by one side or the other or operated with restrictions after relations between the neighbors deteriorated following an armed confrontation on May 28 in which one Cambodian soldier was killed in one of the contested areas.