US President Donald Trump says he has instructed the US Navy to shoot Iranian gunboats "out of the water" if they get too close, a week after vessels from Iran's Revolutionary Guards ventured extremely close to US ships in the Gulf.

Key points: President Donald Trump announced the US Navy's new instructions via Twitter

President Donald Trump announced the US Navy's new instructions via Twitter The move comes a week after 11 Iranian ships came within 9 metres of US vessels in the Gulf

The move comes a week after 11 Iranian ships came within 9 metres of US vessels in the Gulf Mr Trump tweeted just hours after Iran announced the launch of its first military satellite into orbit

"We're not going to stand for it," Mr Trump told reporters at the White House on Wednesday evening, adding such a move would put US ships and sailors in danger.

"That's a threat. When they get that close to our boat, and they have guns, they have very substantial weapons on those boats, but we'll shoot them out of the water."

Earlier in the day, Mr Trump tweeted he had instructed the US Navy to "shoot down and destroy" Iranian gunboats that "harass" them.

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The comments from Mr Trump are the latest in a week where tensions have risen — and the Revolutionary Guards, warned the US not to make a "mistake" in the Gulf.

The President's tweet was then met with a prompt response from a spokesperson for the Iranian armed forces, saying the US should instead focus on saving its military from the coronavirus.

"Today, instead of bullying others, the Americans should put all their efforts toward saving those members of their forces who are infected with coronavirus," Abolfazl Shekarchi said.

Earlier this month, the US military said 11 vessels from Iran's navy came dangerously close to US ships in the Gulf, calling the moves "dangerous and provocative."

At one point, the Iranian vessels came within 9 metres of the US Coast Guard cutter Maui.

Guards says they launched Iran's first military satellite

Mr Trump's tweet came mere hours after the Revolutionary Guard announced it had put the nation's first military satellite into orbit.

There was no immediate independent confirmation of the launch of the satellite, which the Guard called "Noor," or light.

Iran's Republic Guards say the launch is a 'new development in the field of space for Islamic Iran'. ( AP )

The US State Department did not immediately respond to requests for comments, while the Pentagon said it "will continue to closely monitor Iran's pursuit of viable space launch technology."

However, such a launch immediately raised concerns among experts on whether the technology used could help Iran develop intercontinental ballistic missiles.

US officials have said they fear long-range ballistic technology used to put satellites into orbit could also be used to launch nuclear warheads.

Tehran denied US assertions that such activity is a cover for ballistic missile development and says it has never pursued the development of nuclear weapons.

The satellite was orbiting 425 kilometres above the earth's surface, according to a statement on The Guard's website.

"Iran's first military satellite, Noor, was launched this morning from the central desert of Iran. The launch was successful and the satellite reached orbit," state TV said.

The Guards said it used the Qased, or "Messenger", satellite carrier to launch Noor, from Iran's Central Desert, without giving details of the technology.

"The three-stage Qased satellite launcher uses a combination of solid and liquid fuels," it said.

TV footage showed the satellite carrier was inscribed with a verse of the Koran that Muslims often recite when travelling: "Glory to Him who has subjected this to us, as we could never have done it by our own efforts".

A 'strategic achievement'

The Revolutionary Guards report to Iran's Supreme Leader Ayatollah Ali Khamenei and have repeatedly warned that US regional bases and its aircraft carriers in the Gulf are within the range of Iranian missiles.

"This action will be a great success and a new development in the field of space for Islamic Iran," the Guards statement said.

As the world grapples with the coronavirus pandemic and historically low oil prices, the missile launch may signal a new willingness to take risks by Iran.

"This raises a lot of red flags," said Fabian Hinz, a researcher at the James Martin Center for Nonproliferation Studies at the Middlebury Institute of International Studies in Monterey, California said.

"Now that you have the maximum pressure campaign, Iran doesn't have that much to lose anymore," Mr Hinz said.

Mr Hinz said based on state media images, the launch appeared to have happened at a previously unnamed Guard base near Shahroud, Iran, some 330 kilometres northeast of Tehran.

The base is in Semnan province, which hosts the Imam Khomeini Spaceport from which Iran's civilian space program operates.

"Today, the world's powerful armies do not have a comprehensive defence plan without being in space," the head of the Guards, General Hossein said.

"And achieving this superior technology that takes us into space and expands the realm of our abilities is a strategic achievement."

Tensions between the United States and Iran have been heightened since a January drone strike executed by the US killed a top Iranian general in Iraq, Qassem Soleimani.

It was followed by Tehran launching ballistic missiles at American soldiers in Iraq.

The United States argues that such launches by Iran breach United Nations Security Council Resolution 2231, which calls upon Tehran not to undertake activities related to ballistic missiles capable of delivering nuclear weapons, including launches using such technology.

The resolution, which endorsed the nuclear pact between Iran and six major powers, stops short of explicitly barring such activity.

AP/Reuters