BANGKOK/PHNOM PENH - Nine Thai civilians were killed and 14 others injured in military attacks near the Thailand-Cambodia border on Thursday, the Thai army said in a statement.

The Thai army said seven civilian targets in four northeastern Thai provinces were attacked by Cambodian supporting fire weapons, resulting in damage to homes, businesses, crops, and livestock.

The situation escalated following skirmishes that began Thursday morning when Thai and Cambodian troops exchanged fire at a disputed area.

Thailand is closing all border crossings with Cambodia, a spokesperson of Thailand's Ad Hoc Center for Thailand-Cambodia Border Situation told a press briefing on Thursday.

Thailand's Second Army Region also posted on social media that at 10:58 am local time, the Thai army deployed six F-16 fighter jets and destroyed two Cambodian military facilities. 

ALSO READ: Cambodia asks UN court to settle border disputes with Thailand

In Phnom Penh, Cambodian Prime Minister Hun Manet called on the people to stay calm and trust the government and armed forces amid a border clash with Thailand.

In a post on his official social media platforms, Hun Manet said the Thai army launched on Thursday morning an attack on Cambodian army positions in Oddar Meanchey province, and expanded the geographical area of their attack to Preah Vihear province.

"Cambodia has always maintained a position of wanting to resolve issues peacefully, but in this case, we have no choice but to respond with armed forces against armed aggression," he said.

Cambodian Senate President Samdech Techo Hun Sen said that the Thai army shelled the border areas of Oddar Meanchey province and Preah Vihear province.

In a post on his official social media platforms, Hun Sen said Thai soldiers began to attack the Cambodian troops, and the Cambodian soldiers had no choice but to fight back and counterattack.

He urged people not to panic, nor to stockpile rice or other goods, and called on vendors not to increase the prices of goods.

ALSO READ: Thai court suspends PM over leaked call with Cambodian politician

"Thai military had launched first an armed assault on Cambodian forces, and Cambodian forces acted strictly within the bounds of self-defense, responding to an unprovoked incursion by Thai troops that violated our territorial integrity," Lieutenant General Maly Socheata, undersecretary of state and spokesperson for Cambodia's Ministry of National Defense, said in a statement.

The Thai army said the border clash happened after the Cambodian side first opened fire, injuring a Thai soldier.

In a statement, the Thai army said that its task force had detected a Cambodian unmanned aerial vehicle (UAV) flying over Ta Muen temple complex at around 7:35 am local time.

After the UAV activity, a group of six armed Cambodian soldiers advanced towards the barbed wire in front of a Thai operational base, the Thai army said.

Thai soldiers attempted to de-escalate the situation through verbal communication, shouting at the approaching troops to avoid conflict while remaining on high alert, the Thai army said.

The Thai army said Cambodian forces opened fire on a Thai position located about 200 meters east of the main temple at approximately 8:20 am local time.

Thailand's acting Prime Minister Phumtham Wechayachai on Thursday told Thai media that he has been informed of the incident that happened at the border areas with Cambodia and needs to handle the current situation with caution while complying with relevant international laws.

Ties downgraded

Cambodia decided on Thursday to downgrade diplomatic ties with Thailand to the lowest level and recalled all of its diplomatic staff from Bangkok, Cambodian foreign ministry's spokesperson Chum Sounry said.

Thailand had downgraded its diplomatic relations with Cambodia on Wednesday after a landmine near the border injured Thai soldiers. However, Cambodia rejected Thai accusations.

According to a statement released by the Prime Minister's Office, Phumtham ordered to downgrade diplomatic relations by recalling the Thai ambassador to Cambodia and expelling the Cambodian ambassador to Thailand.

ALSO READ: Cambodia, Thailand start talks over border issues after recent skirmish

"Thailand will further consider the level of relationship with Cambodia," the statement said.

Phumtham has also instructed the Thai Ministry of Foreign Affairs to submit a letter of protest to Cambodia regarding the incident.

The Thai army said that five soldiers were injured, one of whom suffered severe injuries to his leg, in a landmine explosion while on patrol in the border area. In a similar incident last week, a landmine explosion near a disputed area wounded three Thai soldiers.

Thailand said the mines were newly planted and accused Cambodia of violating the Anti-Personnel Mine Ban Convention, or the Ottawa Convention.

The situation along the Thailand-Cambodia border has been tense since a brief exchange of gunfire took place in late May that killed a Cambodian soldier.

Cambodia on Wednesday rejected Thai accusations over the injury of Thai soldiers by a border landmine explosion, saying the incident happened because the Thai side strayed from mutually agreed patrol routes. 

READ MORE: Thailand criticizes Cambodia over leaked phone call

"Cambodia has repeatedly reminded the Thai side that these areas still contain many mines and remnants of war that have not been cleared, and urged the Thai side to avoid acting contrary to mutually agreed patrol routes as stated in the 2000 Memorandum of Understanding," said Socheata, the spokesperson for Cambodia's defense ministry.

Socheata said the defense ministry and the Royal Cambodian Armed Forces reaffirmed their full support for the position of the Royal Government of Cambodia in resolving the border issue with Thailand through peaceful means and based on international law.