About 60 people have died and more than half a million have been displaced since hostilities resumed last week between the Southeast Asian neighbours, shattering a ceasefire that President Donald Trump had brokered in late July.
US Secretary of State Marco Rubio called Thai Foreign Minister Sihasak Phuangketkeow on Friday, reiterating Washington's concerns and urging Thailand to de-escalate the situation and return to the ceasefire deal, the State Department said.
Chinese Foreign Minister Wang Yi spoke with his Thai and Cambodian counterparts on Thursday and said both had "expressed their desire to ease tensions and achieve a ceasefire", China's foreign ministry said.
"The intensity of this round of clashes has far exceeded previous incidents, and if it continues, it will benefit neither side and will undermine (Association of Southeast Asian Nations) unity," the ministry said in a statement, adding a special envoy had visited both countries in an effort to restore peace.
The Thai foreign ministry said Sihasak had reaffirmed Bangkok's position to Rubio and "shared information on the way forward", including joining Monday's ASEAN meeting.
The ministry also confirmed the call with Wang.
Cambodia has not commented on the overtures from Washington and Beijing.
Cambodian Foreign Minister Prak Sokhonn is also set to join the meeting in Kuala Lumpur on Monday, which would be the first face-to-face meeting between the governments since the fighting resumed on December 8.
Malaysian Prime Minister Anwar Ibrahim, the ASEAN chair who helped broker the July ceasefire, said this week he was cautiously optimistic about the meeting because the prime ministers of Thailand and Cambodia were both keen to reach an amicable solution.
Thailand and Cambodia accuse each other of moves that led to the breakdown of the July truce, which was expanded into a wider agreement to help settle the conflict in October.
The neighbours have long disputed sections of their 800km land border.
The fighting now stretches from forested inland areas near Laos to coastal provinces.
Fighting continued on Friday across the frontier, with Cambodia firing heavy weapons into some area and Thailand retaliating, a Thai defence ministry spokesperson said.
Tensions had simmered since Thailand in November suspended de-escalation measures - including withdrawing troops and heavy weapons and freeing Cambodian prisoners of war - in response to the maiming of a Thai soldier by a landmine.
Thailand says the mine was among several laid recently by Cambodia, which rejects the allegation.
Bangkok insists that any end to the fighting must start with a cessation of hostilities by the other side and a clear ceasefire proposal, while Phnom Penh maintains that it is defending itself against military actions by its neighbour.
