The US accuses Iran of being behind a drone attack on a chemical tanker in the Indian Ocean.
The attack on the Chem Pluto on Saturday resulted in a fire, but there were no casualties.
Although Iran has not commented on the attack, the US military said the “one-way attack” was carried out by a “drone fired from Iran.”
It would be the first time that the US has accused Iran of directly attacking a ship. It is also believed to be the furthest attack Iran undertakes from its own territory.
Yesterday it accused Iran of supporting Houthi rebels in Yemen, who have targeted commercial ships in the Red Sea.
The accusations come as Iran has threatened to close the Strait of Gibraltar and the Mediterranean Sea if Israel and its allies continue to commit “crimes” in Gaza.
Iran, which has backed Hamas, accused the US and other Western states of supporting Israel's alleged war crimes committed during its ground offensive in the Gaza Strip, where more than 20,000 people have been killed since October 7.
“They will soon await the closure of the Mediterranean Sea, (the Strait of) Gibraltar and other waterways,” Brigadier General Mohammad Reza Naqdi, a senior member of the country's Islamic Revolutionary Corps, said on Saturday.
The Iran-aligned Houthi group, based in Yemen, has attacked several merchant ships sailing through the Red Sea in retaliation against Israel's brutal assault on the Gaza Strip, disrupting global trade and forcing some shipping companies to change routes.
The White House said Friday that Iran was “deeply involved” in planning these attacks.
“They will soon await the closure of the Mediterranean Sea, (the Strait of) Gibraltar and other waterways,” said Brigadier General Mohammad Reza Naqdi, a senior member of the country's Islamic Revolutionary Corps.
The Strait of Gibraltar and the Mediterranean Sea are waterways that carry one-fifth of the world's maritime trade
More than 20,000 people have been killed in Gaza as a result of the Israeli ground offensive against the enclave
While Iran itself does not have direct access to the Mediterranean Sea and it was not clear how the Guard might try to cut it off, Iran-backed allies in Lebanon and Syria have access to these waterways, which account for about a fifth of maritime trade in transport the world.
Naqdi spoke of 'the birth of new resistance forces and the closure of other waterways'.
“Yesterday the Persian Gulf and the Strait of Hormuz became a nightmare for them, and today they are stuck… in the Red Sea,” Naqdi added.
National Security Council spokesperson Adrienne Watson told CNN that the US has intelligence indicating that Iran provided a monitoring system essential to the attacks.
“Iran has the choice to provide or withhold this support, without which the Houthis would struggle to effectively track and attack commercial vessels transiting the Red Sea and Gulf of Aden,” Watson said.
While Iran itself does not have direct access to the Mediterranean Sea and it was not clear how the Guard might try to close it, Iran-backed allies in Lebanon and Syria do have access to these waterways.
“Tactical intelligence provided by Iran has been critical in enabling the Houthi to target maritime vessels since the group began attacks in November,” she added.
But Iran's deputy foreign minister rejected claims that the country was involved in the Houthi attacks.
“The resistance (Huthis) has its own instruments… and acts according to its own decisions and capabilities,” Iranian Deputy Foreign Minister Ali Bagheri told Iran's Mehr news agency.
“The fact that certain powers, such as the Americans and the Israelis, are suffering attacks from the resistance movement… should in no way call into question the reality of the strength of the resistance in the region,” he added .
The Houthis have been fighting Yemen's government since 2014, have seized large swathes of land and are backed by Iran.
Following Israel's retaliatory offensive against the Gaza Strip, the group's leaders declared war on Israel and launched several attacks on Israeli cities, despite being thousands of kilometers away.
Iran has repeatedly warned that Israel's war against Hamas would expand rapidly. Last month, Iranian Foreign Minister Hossein Amir-Abdollahian said the intensity of the war meant its expansion was “inevitable.”
The country's president, Ebrahim Raisi, previously said Iran sees it as “its duty to support the resistance groups,” but stressed that they are “independent in their opinion, decision and action.”
The UK and its allies will not allow the Red Sea to become a 'no go' zone for shipping and will step up efforts to tackle Iran's 'malign influence', ministers have said.
Defense Secretary Grant Shapps said Britain was committed to repelling attacks on ships using the vital trade route by an Iranian-backed group in Yemen.
And Foreign Secretary Lord Cameron said an “incredibly clear message” must be sent to Tehran that its activities will not be tolerated.
Mr Shapps told the Sunday Times: 'We are committed to protecting British interests – ships flying the British flag, or carrying British sailors, or carrying goods destined for our shores.
“We have seen the disruption caused by the terrorist attacks, with major operators, including Maersk and BP, avoiding the region.
“We cannot allow any maritime area to become a no-go area, especially if it concerns a crucial route. But more broadly than that, we must promote a safer world.
“The wave of illegal attacks poses a direct threat to international trade and maritime security.
“The rules-based world order means we must remain committed to fending off these attacks to protect the free flow of global trade, and I am determined that Britain will remain a key player in that.”
Foreign Secretary Lord Cameron said Yemen's Houthi rebels, who have attacked cargo ships along the busy trade route, were just one of several Iranian-backed groups including Hamas.
The attacks on shipping in the Red Sea by the Houthis began in response to the conflict in Gaza, with the group claiming it was targeting ships with Israeli ties.
Further incidents of ships being targeted by drones in the Red Sea were reported on Saturday.
Lord Cameron said: 'Iran has a thoroughly malign influence in the region and in the world – there is no doubt about that.
“You've got the Houthis, you've got Hezbollah, you've got the Iranian-backed militias in Iraq who have actually attacked British and American bases and troops.
'And of course Hamas. So you have all these proxies, and I think it's incredibly important that Iran, first of all, receives an incredibly clear message that this escalation will not be tolerated.
“Second, we must work with our allies to develop a really strong set of deterrents against Iran, and it is important that we do that.
“The level of danger and insecurity in the world is at an extremely high level compared to previous years and decades, and the Iranian threat is part of that picture.”
The United Kingdom Maritime Trade Operations (UKMTO), a Royal Navy initiative that provides security incident information to shipping companies, highlighted a series of attacks on Saturday.
There were multiple reports of a drone flying low over a ship before exploding about 1.5 nautical miles away, with the incident taking place about 50 nautical miles off the coast of Yemen.
Another drone strike was reported in the Red Sea, about 45 nautical miles from Saleef, Yemen.
Another incident on Saturday took place about 200 miles southwest of Veraval, India – well outside the Red Sea, where the attacks on shipping have been focused – with the US claiming that a kamikaze drone launched from Iran struck a chemical tanker.
Lord Cameron's comments followed a visit to the Middle East where he discussed the situation in the Red Sea with his Egyptian counterpart.
The Royal Navy warship HMS Diamond has already joined an international operation to protect cargo ships and Lord Cameron hinted at possible greater British involvement in the coalition.
If the Red Sea is too dangerous for shipping, ships traveling between Asia and Europe will be forced to detour around the southern tip of Africa instead of using the Suez Canal, increasing costs.