After two tankers loaded with petroleum products were attacked in the Gulf of Oman, Iranian officials rejected US claims that Tehran was behind the blasts.
The US accusations were made without "a shred of factual or circumstantial evidence," Iranian Foreign Minister Javad Zarif said on Twitter on Friday.
Previously, the US Navy said it spotted Iranian vessels near the targeted tankers and published a video that it claims shows Iranian sailors removing an unexploded limpet mine from the hull of one of the vessels.
US President Donald Trump said Friday in an interview with Fox News that the incident has "essentially got Iran written all over it... I guess they didn't want the evidence left behind."
However, Iranian Foreign Ministry spokesman Abbas Mousavi said the Iranian navy came to "help" the ships and had "saved" their crews. He dismissed the US claims as "baseless."
Russia's Foreign Ministry warned against assigning blame for the incident until a "thorough and unbiased international probe" had been completed. It added that the US's "Iranophobic" stance had "artificially" fueled tensions.
"We consider it necessary to refrain from hasty conclusions," it said.
UK: Responsibility almost certain lies with Iran
UN chief Antonio Guterres also called for an independent investigation, saying: "It's very important to know the truth. And its very important that responsibilities are clarified."
Later on Friday, UK Foreign Secretary Jeremy Hunt said that Britain's indepdent assessment indicated involvement from Tehran.
"Our own assessment leads us to conclude that responsibility for the attacks almost certainly lies with Iran. These latest attacks build on a pattern of destabilising Iranian behaviour and pose a serious danger to the region."
"No other state or non-state actor could plausibly have been responsible," he added, calling on Iran to "cease all forms of destabilising activity."
'They saw it with their own eyes'
The tanker seen in the black and white video released by the US Navy is the Japanese-owned Kokuka Courageous. While the US Navy referred to a magnetic mine, the head of Kokuka Sangyo shipping company Yutaka Katada said that "something seems to have flew in," according to the ship's crew.
"The crew members are saying that they were hit by a flying object. They saw it with their own eyes," he told reporters in Tokyo. The impact happened above the water line. The crew took "evasive manoeuvres" but were hit again three hours later. There was no damage to goods and fuel, and it is unlikely that the ship would sink, Katada said.
Magnetic limpet mines were previously used by Iran to sabotage oil tankers during the so-called "Tanker War" in the late 1980s.
'Clear signs' Iran is responsible
Guido Steinberg from the German Institute for International and Security Affairs told DW there were "clear signs that the Iranians are responsible."
"It is Iran's modus operandi to use limpet mines and to show the US that they have opportunities to attack the flow of oil in the Persian Gulf and the Strait of Hormuz — but at the same time they are not attacking directly."
The most radical elements in Iran's military are aiming to show that they can "stop the flow of oil" through the Strait of Hormuz in case of a US or a Saudi attack. Almost one-fifth of the world's oil exports — from Saudi Arabia, Iran, the United Arab Emirates (UAE), Kuwait and Iraq — is exported using this route.
The tensions between the US and Iran are already high over the US pullout from the 2015 nuclear accord and the reimposition of economic sanctions. The Thursday blasts resemble a similar attack on four oil tankers in May, which US officials also linked with Iran.
"If this goes on as it has been going on for two months now we will see a military escalation before the end of the Trump administration," Steinberg told DW.
China to hold up Iran ties
The news of the Thursday attacks on the two tankers, one of which is owned by a Japanese company, came as Japanese Prime Minister Shinzo Abe was wrapping up a visit to Iran.
On Friday, Japanese officials in Tokyo said the incident would be discussed on an upcoming G20 meeting involving energy and environment ministers in Osaka. However, Japan's Defense Minister Takeshi Iwaya said that Japan had no intention of sending troops to the Strait of Hormuz region in response to the attacks.
Following the incident, China's President Xi Jinping said Beijing would promote development of ties with Iran regardless of how the situation changes. China's official news agency Xinhua reported that Xi made the pledge while meeting his Iranian colleague, Hassan Rouhani, on the sidelines of a high-profile summit in Kyrgyzstan on Friday.
Rouhani later described the US as a "serious threat to regional and global stability."
dj/amp (dpa, AFP, Reuters, AP)