Diplomatic efforts gained momentum on Tuesday toward a second round of high-level talks between the US and Iran, even as Washington imposed a naval blockade on Iranian ports.

Despite the collapse of talks between the two adversaries on Sunday, United States Vice-President JD Vance, who led the US delegation, told Fox News on Monday that his country "made a lot of progress" by communicating to Tehran where the US "could make some accommodation".

"I really think the ball is in the Iranian court, because we put a lot on the table," Vance said, as a second US official confirmed continuing efforts to salvage a diplomatic agreement.

The developments come as the US blockade took effect on Monday, with Iran issuing a credible retaliation threat that has set up a new standoff — posing severe risks to the global economy and raising the specter of a ceasefire collapse and resumption of full-scale hostilities.

The International Energy Agency warned on Tuesday that demand for crude oil will likely see the biggest slump in the second quarter since the pandemic slammed the global economy in 2020.

Meanwhile, US aircraft carrier USS George H. W. Bush is sailing via the African coast toward the Arabian Sea, avoiding the Red Sea and Bab el-Mandeb Strait, according to US Naval Institute News. The route bypasses the shortcut waterways where Yemen's Houthi militants launched drone and missile attacks on US vessels in 2024 and 2025.

An Iranian military spokesman labeled any US restrictions on international shipping "illegal and constitute piracy", warning that if Iranian ports came under threat, no port in the Persian Gulf or Gulf of Oman would remain secure.

US President Donald Trump has insisted any final deal must include ending Iran's ability to develop a nuclear weapon, while Iran has reaffirmed that its nuclear program is exclusively for civilian purposes.

"I can tell you that we've been called by the other side," Trump told reporters. "They'd like to make a deal. Very badly, very badly."

Media reports said on Monday that the US pressed for a 20-year suspension of Iran's uranium enrichment program during weekend negotiations in Islamabad, Pakistan. Iran, in turn, proposed a five-year freeze on its nuclear activities — a proposal US officials rejected, The New York Times reported.

'All-out efforts'

Diplomatic efforts were also stepping up elsewhere, with Pakistani Prime Minister Shehbaz Sharif saying on Monday that "all-out efforts are underway" to reach a deal to halt the fighting and that the ceasefire was "holding".

Hadi Golriz, head of the press of Iran's embassy in Islamabad, told Xinhua News Agency on Tuesday that the upcoming rounds of talks could take place at any time and anywhere, but nothing is official as of now.

Some media reports on the next round of talks are "baseless", he said. Earlier on Tuesday, Reuters quoted multiple sources as saying that the two sides could return to the Pakistani capital later this week.

Mohamad Elmasry, professor at the Doha Institute for Graduate Studies, said both the US and Iran appear to seek an "off-ramp from the war" but need a "face-saving" way to exit.

"This war has been extremely costly for the parties involved and far beyond," he told Al Jazeera. "Iran has greater leverage than it did at the start of the war, but I have no doubt they would seek an end to hostilities."

Iran's President Masoud Pezeshkian said earlier that Tehran "will only continue negotiations within the framework of international law", state broadcaster IRIB reported.

Kremlin spokesman Dmitry Peskov said on Tuesday that Russia's offer to take Iran's enriched uranium as part of a potential US-Iran deal remains on the table.