The Ministry of External Affairs (MEA) said there is no legally valid boundary between Pakistan and China concerning Indian territory and described the commission as having "no legal basis".
"The entire Union Territories of Jammu & Kashmir and Ladakh have been, are and will always remain integral and inalienable parts of India," the MEA said.
"Pakistan has no locus standi to enter into arrangements concerning Indian territory under its illegal and forcible occupation," it added.
India Rejects 1963 China-Pakistan Boundary Agreement
New Delhi also rejected the so-called China-Pakistan Boundary Agreement signed on March 2, 1963, which purportedly demarcated the border between China's Xinjiang region and Pakistan-occupied Gilgit-Baltistan.
India described the agreement as "illegal" and "invalid".
"We resolutely oppose and reject any attempts to alter the status of these occupied territories or legitimise illegal occupation, impinging on India's sovereignty and territorial integrity," the Foreign Ministry said.
It further said that any boundary cooperation between China and Pakistan involving what India regards as its territory is "completely unacceptable" and would not affect India's sovereignty over these areas.
India tells Pakistan to vacate occupied territories
India also called on Pakistan to stop "engaging in such theatrics" and demanded that it vacate territories under what New Delhi describes as its illegal and forcible occupation.
The statement came after Pakistan's Foreign Ministry announced the first meeting of the Pakistan-China Boundary Joint Commission in Islamabad and described it as a "significant milestone" in bilateral relations.
Pakistan-China commission promises border cooperation
According to Pakistan's Foreign Ministry, the commission is expected to facilitate greater cooperation between the two countries, including joint border surveys, trade flows and connectivity.
The inaugural meeting was held at Pakistan's Ministry of Foreign Affairs and was co-led by Li Ya, Deputy Director General of the Chinese Foreign Ministry's Department of Boundary and Ocean Affairs, and Bilal Mahmood Chaudhary, Director General (China) in Pakistan's Foreign Ministry.
India's rejection makes clear that New Delhi does not recognise the legitimacy of arrangements between Pakistan and China concerning territories it claims as an integral part of India.