He said the protests were submitted to the prime minister of Malaysia, in his capacity as ASEAN chair, and to the United States and China, which are serving as observers in the Thai-Cambodian border dispute.
The move followed reports that Cambodian forces continued firing along the border despite the ceasefire agreement reached on July 28, reports the Bangkok Post.
The agreement was intended to halt all hostilities as of midnight on July 29.
While declining to disclose the contents of the letters, Mr Maris said the Thai government had lodged protests against Cambodia under available frameworks, including its use of anti-personnel landmines banned under the Ottawa Convention.
He said Thailand also addressed the United Nations Security Council and affirmed that it exercised its legitimate right to respond to violations of its sovereignty with restraint and within the bounds of international law.
Cambodia broke truce: RTA
The Royal Thai Army (RTA) yesterday accused and condemned Cambodia of intentionally breaking the ceasefire agreement, which took effect at midnight, by firing shots at many Thai locations afterwards.
The RTA said in a statement that Cambodia, after midnight, opened fire at Thai locations in the Chong Arn Ma, Chong Bok, Prasat Ta Kwai, Phu Makheu and Sam Tae areas.
“That shows an intention to violate the (ceasefire) agreement and ruin a mutual trust system. The army condemns the act,” said RTA spokesman Maj Gen Winthai Suvaree. Thailand took retaliatory measures in accordance with its right to self-defence, he said.
He said Thailand did not invade anywhere. It was blocking incursions and protecting its sovereignty in compliance with international rules.
Thailand complied with the ceasefire agreement as it stopped firing immediately at midnight, Maj Gen Winthai said.
Col Richa Suksuwanon, deputy army spokesperson, said the RTA received reports from the Suranaree Task Force of renewed hostilities during the early hours of yesterday.
According to these reports, shortly after the ceasefire was supposed to take effect, Cambodian troops launched provocations in the Phu Makheu area of Si Sa Ket, prompting retaliatory fire from Thai troops. The exchange of gunfire continued into the morning.
A similar confrontation occurred in the Sam Tae area of Kantharalak district, also in Si Sa Ket, where gunfire reportedly lasted until 5:30am, said Col Richa, adding Cambodian forces also fired explosives throughout the night.
In Surin province, the 2nd Army Region reported explosions near the Ta Kwai temple ruins in Phanom Dong Rak district at 3am and again at 5am.
Video footage taken by military personnel at 6:29am yesterday appeared to capture ongoing gunfire in the background, further corroborating the reported clashes.
11 key sites secured: TCBSAC
RAdm Surasan Kongsiri, spokesman for the Thai-Cambodian Border Situation Administration Centre (TCBSAC), said Thai forces had secured 11 key locations along the Thai-Cambodian border as yesterday morning.
They were Phu Makheu, Chong Arn Ma, Ta Muean Thom, Prasat Ta Kwai, Chong Bok, Don Tuan, Sattasom, Chong Chom, Chong Sai Ta Ku in Ban Kruat district of Buri Ram, Preah Vihear and Phran Yao.
He said the conflict resulted in the displacement of over 188,000 civilians, 15 civilian deaths, 12 critically injured, 13 moderately injured and 13 with minor injuries.
RAdm Surasan said the TCBSAC also condemned Cambodia for using ancient ruins as shields, and the act was a violation of Unesco guidelines.
The 2nd Army Region Tuesday detained 18 surrendering Cambodian soldiers following the clash in the Samtae area of Kantharalak district in Si Sa Ket and upheld humanitarian principles for the care and medical treatment of wounded personnel.
Maj Gen Winthai said the incident occurred after Cambodia employed heavy and other weapons, firing into Thai territory. The Thai side deployed the Cavalry Battalion Task Force to conduct counter-operations and clear Cambodian positions.
Containing damage: Phumtham
Acting Prime Minister Phumtham Wechayachai blamed the breach of the ceasefire agreement on poor communication or a lack of discipline from the Cambodian side.
He said the unconditional ceasefire was agreed to allow for the conflict resolution process to continue, and discussions will be conducted under the bilateral mechanisms of the Regional Border Committee (RBC) and the General Border Committee (GBC).
Mr Phumtham said the army’s proposal at the July 28 meeting was accepted in principle.