For decades, India has refused to recognise a Pakistan-China boundary in territory it claims as its own.

Last week, Pakistan and China moved to institutionalise one, prompting a sharp response from Delhi.

The two countries operationalised the Pakistan-China Boundary Joint Commission, which Pakistan described, external as a “significant milestone” that would deepen cooperation on border management, joint surveys, trade and people-to-people connectivity.

India reacted sharply, external, rejecting the move as having no legal basis, saying it did not recognise any Pakistan-China boundary involving territory it claims as Indian.

The announcement comes at a particularly sensitive moment.

India and China are seeking to stabilise their relationship after years of military tensions along the Line of Actual Control (LAC), the disputed line separating their forces along much of their Himalayan frontier. At the same time, Beijing and Islamabad are deepening cooperation along a neighbouring stretch of the frontier that India also claims.

“There is no boundary between Pakistan and China. We reject the so-called Joint Commission, which is without any legal basis,” Indian foreign ministry spokesman Randhir Jaiswal said.

The commission concerns the Pakistan-China frontier, including the Shaksgam Valley, a roughly 5,180 sq km tract that Pakistan ceded to China in 1963 but which India claims as part of its territory in Ladakh.

India says the territory was part of the former princely state of Jammu and Kashmir and was illegally occupied by Pakistan before being ceded to China. The Indian government has never recognised the agreement and considers it illegal and invalid.

This history explains the particular sensitivity of Wednesday’s announcement.

“Pakistan has no locus standi to enter into arrangements concerning Indian territory under its illegal and forcible occupation,” the Indian foreign ministry said.

Pakistan says Jammu and Kashmir remains a disputed territory, and argues that India therefore has no standing to challenge its 1963 boundary agreement with China. It regards the agreement as valid.

Jabin T Jacob, professor at the Department of International Relations and Governance Studies at Delhi’s Shiv Nadar University, said the new development represented the revival of an old mechanism rather than an entirely new arrangement.

“A joint boundary commission is provided for in the 1963 Sino-Pak Agreement, the only issue at hand is the timing of its operationalisation,” he told the BBC.

He said there could be several reasons for the timing, including China’s broader effort to demarcate its boundaries and a desire to institutionalise exchanges and movement along a frontier at a time when Pakistan’s other borders have experienced conflict and instability.

Jacob said India should be “worried” by the development. More importantly, he said, the move appeared to disregard a provision in the 1963 treaty itself.

Article 6 of the agreement provided for its renegotiation once the Kashmir dispute was settled with whichever country ultimately controlled the territory, Jacob said.

For India, Jacob said, the problem is compounded by the international information environment.

“China’s relative dominance of the international media and information landscape – [with] CGTN, CRI, presence on social media – relative to India allows it to put forward its narrative and maps globally while India is limited to fulminations that other world capitals are likely to ignore,” he said.

That concern is distinct from the practical management of the frontier itself. Pakistan and China already have extensive infrastructure and connectivity links across the region, including the China-Pakistan Economic Corridor (CPEC) and the Karakoram Highway.

Husain Haqqani, former Pakistani ambassador to the US and now a senior fellow at Anwar Gargash Diplomatic Academy and Hudson Institute, said the new commission was both practical and political.

“It is a combination of both,” Haqqani told the BBC. “It is a mechanism to enhance border and boundary cooperation, prevent illegal crossings and protect the strategic infrastructure tied to CPEC.”

He said it also served as a signal to India that Beijing continued to view Kashmir through the Pakistani prism.

“China has never accepted India’s position on Kashmir and China views Gilgit-Baltistan from the Pakistani, not Indian prism,” Haqqani said, referring to the region in Pakistan-administered Kashmir that borders China and which India claims as part of its territory.

Haqqani said Islamabad’s position had evolved in response to developments in Indian-administered Kashmir.

“Pakistan still maintains that the final status of Jammu and Kashmir is yet to be decided,” he said. “But since India has made internal changes – for example, the abrogation of Article 370 – in its part of Kashmir, Pakistan sees no issue with simply institutionalising what has been de facto with China since 1963.”

For Beijing, the arrangement also fits into a broader pattern of using its relationships with neighbouring states to manage and signal its position towards India.

Haqqani said reassurance to Pakistan on Kashmir was of both strategic and geopolitical value to Beijing.

“On the strategic front it further deepens ties with Pakistan and on the geo-strategic front it reinforces for India its fear of a two-front threat from China and Pakistan, which pleases Pakistan and benefits China.”

The timing of the statement, say experts, is also significant.

“China always plans its decisions months, if not years, in advance so the decision to operationalise a joint boundary commission must have been made some time back,” says Haqqani.

“The release of this information was timed for after President Xi Jinping’s recent Brics summit trip to send Pakistan a message of reassurance in the strategic partnership, and India a reminder that multilateral engagement does not translate into any change in China’s vision for South Asia.”

But Jacob cautioned against interpreting every aspect of the development as a direct military move against India.

“There aren’t any immediate or apparent implications for the LAC as of now,” he said.

That suggests that the significance of last week’s announcement may lie less in an immediate change to the disputed Himalayan frontier than in the gradual institutionalisation of arrangements that India has consistently rejected.

India’s position, Jaiswal said, remained “clear and consistent”: any attempt to legitimise what Delhi considers Pakistan’s illegal occupation of Indian territory is unacceptable and has no bearing on India’s sovereignty.

But Haqqani believes the dispute goes beyond the legalities of borders.

“The key disagreement between India and China about the border and boundary is geo-strategic, not cartographic,” he said. “So there is a limit to what border negotiations and border management mechanisms can achieve.”

Pakistan, he added, remained “China’s secondary deterrent against India” – and Beijing’s engagement with Islamabad would continue to send that message to Delhi.