Hopes for a peace deal with Iran faded on Tuesday after the United States said a truce was "on life support", as Tehran rejected a US proposal and hinted that a possible retaliation over further US-Israeli strikes could be uranium enrichment to 90 percent purity.

US President Donald Trump said on Monday that Iran's counteroffer has put the April 8 ceasefire at severe risk.

"I would call it the weakest right now, after reading that piece of garbage they sent us. I didn't even finish reading it," he told reporters. "The ceasefire is on massive life support."

In response, Iran's Parliament Speaker Mohammad Bagher Ghalibaf said his country's armed forces stand ready to deliver a lesson-teaching response to any act of aggression.

"There is no alternative but to accept the rights of the Iranian people as laid out in the 14-point proposal," he said in a post on X on Tuesday.

Also on Tuesday, Ebrahim Rezaei, spokesman for the Iranian Parliament's National Security and Foreign Policy Commission, said Iran could enrich uranium up to 90 percent purity — a level considered weapons-grade — if its territory faces fresh military attacks. "We will review it in Parliament," he said.

The latest twists further roiled global energy markets, already disrupted by the Middle East crisis and the overlapping blockades around the Strait of Hormuz — a critical oil and gas transit route that carries about 20 percent of the world's oil shipments.

The benchmark Brent crude oil futures extended gains on Tuesday, climbing to almost $108 a barrel.

"The energy supply shock that began in the first quarter is the largest the world has ever experienced," Amin Nasser, CEO and president of Saudi Arabia's oil giant Aramco, told investors, warning it would take months for markets to rebalance even if the strait opens immediately.

"If its opening is delayed by a few more weeks, then normalization will last into 2027," he said.

The US Department of Energy said on Monday it is releasing 53.3 million barrels of crude from the Strategic Petroleum Reserve to energy firms under a global arrangement aimed at easing supply tightness, Reuters reported.

Respective demands

Washington had proposed an immediate halt to fighting before negotiating more divisive issues, including Iran's nuclear program. Tehran, however, demanded a full end to hostilities across all fronts — including in Lebanon, where Israel was continuing military strikes.

Iran also insisted on its sovereignty over the Strait of Hormuz, compensation for war damages and an end to the US naval blockade, among other preconditions.

Negotiations between Iran and the US are stuck in a deadlock amid an extremely dangerous situation, Giorgio Cafiero, a Washington-based political analyst, told Al Jazeera.

"The understatement of the century is that the ceasefire is very fragile," he said, adding any "slight miscalculation" could trigger a protracted conflict that could eventually spiral into a messy quagmire.

Iran, the US and Israel reached a ceasefire last month following 40 days of hostilities sparked by joint US-Israeli strikes on Feb 28.

Following the truce, Iranian and US delegations held one round of peace talks in Pakistan on April 11 and 12, which yielded no breakthrough. In recent weeks, the two sides have exchanged multiple proposals aimed at ending the conflict, mediated by Pakistan.

In Lebanon, local leaders have urged the US ambassador in Beirut to press Israel to halt its aerial bombardment.

Israeli strikes on a town in southern Lebanon killed six people and wounded seven others, the National News Agency reported on Tuesday, as fighting continued despite a ceasefire agreement.

Lebanon's Health Ministry told Agence France-Presse on Tuesday that Israeli strikes have killed 380 people since the ceasefire began on April 17.

A ministry official said that "380 people, including 22 children and 39 women, have been killed in strikes on Lebanon since the ceasefire came into effect", out of a total of around 2,900 people killed since the war erupted on March 2.

Meanwhile, US Ambassador to Israel Mike Huckabee said on Tuesday that Israel sent its homegrown Iron Dome anti-missile batteries, along with personnel to operate them, to the United Arab Emirates. The UAE did not immediately comment on his remarks.