The deadline passed on Monday for the start of a US military blockade of ships leaving Iran’s ports, and Tehran threatened to retaliate against ports of its Gulf neighbours after weekend talks ​on ending the war broke down.

Oil prices climbed over $100 per barrel, with no sign of a swift reopening of the Strait of Hormuz to ease the biggest ever disruption ‌in supplies and broader concerns over the durability of a two-week ceasefire agreement reached last week.

Since the war started on February 28, Iran has effectively shut the strait to all vessels except its own, saying passage would be permitted only under Iranian control and subject to a fee.

US President Donald Trump said Washington would block Iranian vessels and any ships that paid such tolls and that any Iranian “fast-attack” ships that went near the blockade would be eliminated. US Central Command said the ​measure would take effect from 10 a.m. ET (1400 GMT) on Monday.

Brigadier General Reza Talaei-Nik, a spokesperson for Iran’s Ministry of Defence, warned that efforts by foreign military to police the strait ​would escalate the crisis and instability in global energy security.

NATO allies, including Britain and France, said they would not be drawn into the conflict by taking part ⁠in the blockade, stressing instead the need to reopen the waterway, through which about one-fifth of the world’s oil normally passes.

The ceasefire that halted six weeks of U.S. and Israeli airstrikes looked in jeopardy, ​with only a week left to run. Washington said Tehran rejected its demands at weekend talks in Islamabad, the highest-level discussions since Iran’s 1979 Islamic Revolution.

BLOCKADE OF IRANIAN PORTS

The US military’s regional Central Command said ​the blockade would be “enforced impartially against vessels of all nations” entering or leaving Iranian ports in the Gulf and the Gulf of Oman.

“The blockade will not impede neutral transit passage through the Strait of Hormuz to or from non-Iranian destinations,” Central Command said in a note to seafarers seen by Reuters on Monday.

Two Iranian-linked tankers, the Aurora and New Future, laden with oil products, left the strait on Monday before the deadline, according to LSEG data.

An Iranian military spokesperson called any US ​restrictions on international shipping “piracy,” warning that if Iranian ports were threatened, no port in the Gulf or Gulf of Oman would be secure. Any military vessels approaching the strait would violate the ceasefire, Iran’s Revolutionary ​Guards said.

Trump said that Iran’s navy had been “completely obliterated” during the war, adding that only a small number of “fast-attack ships” remained.

“Warning: If any of these ships come anywhere close to our BLOCKADE, they will be immediately ELIMINATED, using ‌the same system ⁠of kill that we use against the drug dealers on boats at Sea. It is quick and brutal,” Trump wrote on social media, referring to the U.S. strikes carried out against suspected drug boats in the Caribbean and Pacific.

LEBANON FACES ATTACKS

Trump has also lashed out at U.S.-born Pope Leo, denouncing him as “terrible” in a rare direct attack on the pontiff, who has spoken out against the war.

With the war unpopular at home and rising energy prices causing political blowback, Trump paused the US-Israeli bombing campaign last week after threatening to destroy Iran’s “whole civilisation” unless it reopened the strait.

Israel has continued to bombard Iran-backed Hezbollah in Lebanon and ​on Monday Israeli troops launched an attack to seize a ​key south Lebanon town from the group. ⁠Israel and the US have said the campaign against Hezbollah was not part of the ceasefire, while Iran has insisted it is.

Iran has brought new demands, including recognition of its control of the waterway, lifting of sanctions and the withdrawal of forces from US military bases across the Middle East.

Pakistani Prime Minister Shehbaz ​Sharif said efforts were still on to resolve the conflict after the direct talks between the US and Iran in Islamabad at the weekend.

Trump has ​declared victory, despite failing to ⁠achieve the objectives he set out at the start of the war: to eliminate Iran’s ability to strike its neighbours, end its nuclear programme and make it easier for Iranians to topple their government.

OIL BENCHMARKS UNDERSTATE DISRUPTION

Benchmark oil prices, which had eased last week after the ceasefire was announced, traded around 5% higher on Monday, off the day’s highs but still above $100 a barrel.

Traders say the main benchmarks - used to set prices for trillions ⁠of dollars’ worth ​of commodities worldwide — actually understate the severity of a disruption with no precedent in modern times.

Trump has long said a ​bump in US gasoline prices would be short-lived. But he told Fox News’ “Sunday Briefing” that they could stay high through November’s midterm elections.

Iran’s chief negotiator, Mohammad Bagher Ghalibaf, posted a map of Washington-area gasoline prices on social media with the comment: “Enjoy the current pump ​figures. With the so-called ‘blockade’. Soon you’ll be nostalgic for $4–$5 gas.”

NO COUNTRY HAS RIGHT TO CLOSE HORMUS

Meanwhile, the head of the UN maritime agency said no country had a legal right to block shipping in the Strait of Hormuz, a trade passage paralysed by the US-Iran war.

The International Maritime Organisation’s Secretary General, Arsenio Dominguez, addressed a news conference as access to the strait remained blocked six weeks after the war erupted with US and Israeli strikes against Iran.

The United States had threatened to begin a blockade on Monday of Iranian ports in and around the strait, which Tehran’s forces have been controlling access to since after the war broke out on February 28.

“In accordance with international law, no country has the right to prohibit the right of innocent passage or the freedom of navigation through international straits that are used for international transit,” Dominguez said.

Iranian authorities have been allowing a trickle of vetted vessels to pass the strait through a route close to their coast and, in some cases, have reportedly levied a payment to let vessels through.

“This principle of introducing a toll on an international strait for international navigation is against the international law of the sea and the customary law,” Dominguez said.

“It will create a very dangerous precedent.”

The US vow to blockade Iranian ports, meanwhile, “doesn’t make it any easier”, he added.

“De-escalation is what is going to start helping us to address the crisis and to bring shipping back to the way that we used to operate.”

He predicted that the extra impact of a US blockade on shipping would be negligible, however.

“With the very small number of ships that have managed to transit, an additional blockade is not going to exacerbate the situation in a level that it could be perceived.”