At least 14 people have been killed in Thailand and another in Cambodia in fighting between Thai and Cambodian troops, authorities say, as more than 120,000 people living along both sides of their border flee the ongoing violence.

Deadly fighting continued for a second day on Friday as both countries traded heavy artillery and rocket fire in the bloodiest military confrontation between the two Southeast Asian neighbours in more than a decade.

“The situation has intensified and could escalate into a state of war,” acting Thai Prime Minister Phumtham Wechayachai told reporters.

Cambodian Prime Minister Hun Manet said he had backed a ceasefire proposal put forward by his Malaysian counterpart and chairperson of the Association of Southeast Asian Nations (ASEAN), Anwar Ibrahim, but added that Thailand withdrew its backing of the plan after initially agreeing to it.

In a Facebook post, Hun Manet described Thailand’s decision as “regrettable”.

“The key to resolving the current armed conflict between Thailand and Cambodia is the genuine willingness of the Thai side to accept a ceasefire,” Hun Manet said.

Thailand’s foreign ministry said later that it agreed in principle with the Malaysian proposal for a ceasefire and will consider the plan, but that it must be based on “appropriate on-the-ground conditions”.

“It must be stated that throughout the day, Cambodian forces have continued their indiscriminate attacks on Thai territory,” the ministry said in a post on X. “Cambodia’s actions demonstrate a lack of good faith and continue to place civilians in danger.”

Speaking to Al Jazeera earlier on Friday, a spokesman for the Thai Ministry of Foreign Affairs, Nikorndej Balankura, said while Thailand insists it has the tools to resolve the issue bilaterally, it has not ruled out future mediation by regional partners.

“Our doors have always been open to talks. … We are still waiting for positive reactions from the Cambodian side,” Nikorndej said.

On possible third-party mediation, he added: “It’s a bit too premature for me right now to say that we are ready for any mediation, … but if we are going to talk about anyone to step in and help, countries in ASEAN … would be best suited.”

A Thai military official said on Friday that attacks have been reported in 12 locations along the disputed border, up from six a day earlier, indicating a widening of the fighting.

Rear Admiral Surasant Kongsiri, a military spokesperson, said during a news conference that Cambodia had continued to use heavy weapons.

Meanwhile, Thailand’s Ministry of Public Health reported at least 13 civilians and one soldier were killed in Thailand when fighting broke out on Thursday.

A local official in Cambodia’s Oddar Meanchey border province told the Reuters news agency that one person was killed and five wounded in Thai attacks.

More than 120,000 displaced

Quoting officials in Cambodia’s Preah Vihear province, the Khmer Times newspaper said about 20,000 residents have evacuated from the country’s northern border with Thailand.

Meanwhile, Thailand has moved 100,672 people from four provinces bordering Cambodia to shelters, Thailand’s Ministry of Interior was cited as saying by the AFP news agency. It has also opened more than 300 evacuation centres, according to officials.

Thailand also declared martial law on Friday in eight districts along the border, effective immediately.

Reporting earlier from Surin province near the Cambodian border, Al Jazeera’s Tony Cheng said the government described the frontier as “very long and porous”, complicating efforts to track the movement of displaced people.

“It is very hard to see how many people are here in the evacuation centre … because there are people arriving all the time,” he said.

Thai authorities said they are meeting the immediate needs of those seeking refuge by providing food, water and medical care at the temporary shelters. However, local accounts painted a grim picture.

“Some of the older people that we have talked to said what they have seen in the last 48 hours – the fighting they’ve seen – has been the fiercest in this disputed area since the late 1970s when the Khmer Rouge had complete control of the other side of the border,” Cheng reported.

The violence, centred around a contested section of the Thai-Cambodian border, has prompted calls for calm from regional actors. “People are trying to talk down both sides, urging leaders to de-escalate,” Cheng added.

UN to hold emergency meeting

Diplomatic sources told AFP that the United Nations Security Council will hold an emergency meeting on Friday to discuss the border fighting.

On Thursday, Thailand said it scrambled an F-16 fighter jet to bomb targets in Cambodia, whose military said its forces launched long-range rockets towards civilian areas along the Thai border.

Both countries have blamed each other for starting the fighting.

The United States, a longtime treaty ally of Thailand, has called for an immediate end to the hostilities.

China, a close ally of Cambodia, said it was deeply concerned about the conflict and hoped both countries “will properly solve their dispute through dialogue and consultation”.

Chinese Foreign Minister Wang Yi said Beijing is ready to play a constructive role in helping de-escalate tensions.

“The root cause of this issue lies in the lingering consequences left by Western colonialists in the past, and it now needs to be faced calmly and handled properly,” he said during a meeting with ASEAN Secretary-General Kao Kim Hourn in Beijing, according to a statement from the Chinese Ministry of Foreign Affairs.

The territorial dispute between the two neighbours largely stems from a 1907 map drawn under French colonial rule, which was used to demarcate Cambodia’s boundary with Thailand.