UN Secretary-General Antonio Guterres is concerned by reports of renewed armed clashes between Cambodia and Thailand, particularly the reported airstrikes and mobilization of heavy equipment in the border area, his spokesperson said Monday.

The border dispute between Cambodia and Thailand has already resulted in significant civilian casualties, damage to civilian infrastructure, and displacement on both sides of the border, spokesperson Stephane Dujarric said in a statement.

The UN chief stresses that both parties must protect civilians and facilitate humanitarian relief, and urges both parties to exercise restraint and avoid further escalation, the spokesperson said.

Dujarric said the secretary-general reiterates his call on the parties to return to the framework of the Joint Declaration signed on Oct. 26, recommit to the ceasefire, and implement de-escalation and confidence-building measures.

Guterres calls on both parties to make full use of all mechanisms for dialogue to find a lasting solution to the dispute through peaceful means, the spokesperson said.

"The United Nations stands ready to support all efforts aimed at promoting peace, stability, and development in the region," Dujarric said.

Border clashes broke out again between Thailand and Cambodia from Sunday to Monday, with artillery fire reported in several areas and residents rushing to evacuate in multiple provinces, less than two months after the two countries signed a joint peace declaration.