Iran and the United States on Sunday failed to reach an agreement to end the war in the Middle East as US intelligence pointed to China quietly preparing to deliver new air defense systems to Tehran — raising the stakes of a conflict that may be far from over.

US Vice President JD Vance said after marathon talks in Islamabad, Pakistan that he was leaving after giving Iran the “final and best offer.”

Vance said Washington was seeking a “fundamental commitment” from Iran that it would not develop a nuclear weapon, but that “we haven’t seen that” after holding the highest-level meeting between the two sides since the 1979 Islamic revolution.

After 21 hours of negotiations, no deal emerged — only a pause, a proposal and deepening mistrust.

“We leave here with a very simple proposal, a method of understanding that is our final and best offer. We’ll see if the Iranians accept it,” Vance said before departing Pakistan.

But as diplomats traded ultimatums, intelligence assessments point to a parallel track unfolding far from the negotiating table — one that could reshape the battlefield if talks collapse.

Plausible deniability

Multiple sources familiar with recent intelligence evaluations said China is quietly preparing to transfer new air defense systems to Iran in the coming weeks, a move that could significantly blunt US and Israeli air superiority if fighting resumes.

The systems, described as shoulder-fired anti-air missiles, are designed to target low-flying aircraft — precisely the kind used in close air support and strike missions during the five-week war that began on 28 February.

Officials believe the shipments are being routed through third countries to obscure their origin, allowing Beijing to maintain plausible deniability while reinforcing Tehran’s defenses.

The United States has agreed to a two-week pause in attacks with Israel to allow negotiations to proceed, but intelligence suggests Iran may be using the lull to rebuild and rearm.

Iran’s state broadcaster IRIB said negotiations stalled over “unreasonable demands of the American side,” while its foreign ministry signaled tempered expectations, noting that “no one” could have expected a deal after 40 days of war in a single session.

On the ground, leverage remains tied to geography. Iran’s control over the Strait of Hormuz — through which roughly one-fifth of global oil once flowed — has already rattled markets and pressured Washington.

‘We’ve won’

US President Donald Trump struck a defiant tone during the talks.

“Whether we make a deal or not makes no difference to me. The reason is that we’ve won,” Trump said, citing battlefield gains, including the destruction of key Iranian military assets and death of Iranian leaders.

Yet even as Washington projects confidence, the prospect of enhanced Iranian air defenses complicates any renewed military calculus.

During the war, a US F-15E fighter jet was downed by a heat-seeking missile in an incident that raised questions about the evolution of Iran’s defensive capabilities.

A direct transfer of such systems from China would mark a significant escalation.

While Chinese firms have long supplied dual-use technologies to Iran, a state-backed delivery of weapons systems would signal a deeper, more overt level of involvement.

Beijing, however, has publicly denied any such move, insisting it has “never provided weapons to any party to the conflict” and urging restraint.

Deadlocked

Analysts say China has little interest in openly confronting the United States militarily but sees value in quietly sustaining Iran as a strategic partner, particularly as a major supplier of oil.

Pakistan, which hosted the talks, urged both sides to preserve the fragile ceasefire. Foreign Minister Ishaq Dar said efforts would continue “to facilitate engagement and dialogue” and stressed that it was “imperative” to uphold the truce.

But the negotiations in Islamabad revealed how far apart the sides remain. Iran is demanding the lifting of sanctions and an end to Israel’s war in Lebanon — conditions Washington has ruled out.

“Our experience in negotiating with the Americans has always been met with failure and broken promises,” Iranian parliamentary speaker Mohammad Bagher Ghalibaf said.