The United States is preparing to send hundreds of troops to Saudi Arabia where satellite images appear to show a build up of American forces on the ground.

Up to 500 soldiers are to be sent to the Prince Sultan Airbase in the desert to the east of the capital Riyadh, two officials told CNN, speaking on condition of anonymity.

Preparations are also reportedly underway for a large missile installation from which Patriot surface-to-air missiles can be launched to protect the base from incoming threats.

The moves would likely strengthen the US' controversial relationship with Saudi Arabia, while also responding to rising tensions with Iran which escalated dramatically in recent months.

After the US unilaterally withdrew from a landmark 2015 nuclear deal last year and reimposed tight sanctions, Iran announced in July that it had surpassed limits on enriched uranium imposed in the agreement. The country insists it is not trying to build nuclear weapons.

A standoff has also ensued in the Gulf, with sabotage attacks on foreign tankers, blamed on Iran by the US. In the latest incident Tehran said it had seized a foreign-owned vessel suspected of being used for oil smuggling out of the country/

Tensions high as Trump approves new Iran sanctions: In pictures Show all 17 1 /17 Tensions high as Trump approves new Iran sanctions: In pictures Tensions high as Trump approves new Iran sanctions: In pictures Iran claims that in this picture released by Iran state TV, their surface-to-air missile is seen as it shoots down a US surveillance drone EPA Tensions high as Trump approves new Iran sanctions: In pictures This photo shows US RQ-4A Global Hawk unmanned surveillance drone. A drone of this model was shot down by Iran on Thursday 21 June AFP/Getty Tensions high as Trump approves new Iran sanctions: In pictures An oil tanker is on fire after it was subject to a suspected attacked at the Gulf of Oman on June 13. The US has blamed Iran for the attack Reuters Tensions high as Trump approves new Iran sanctions: In pictures Iran claims that in this picture released by Iran state TV, debris from the downed US drone is seen after it was recovered from Iranian waters AFP/Getty Tensions high as Trump approves new Iran sanctions: In pictures Smoke billows from an oil tanker after it was subject to a suspected attacked at the Gulf of Oman on June 13 Reuters Tensions high as Trump approves new Iran sanctions: In pictures US President Trump holds up a signed executive order to increase sanctions on Iran on 24 June AP Tensions high as Trump approves new Iran sanctions: In pictures Iranian President Rouhani stated in a televised address that the White House is "afflicted by mental retardation" following the increase in sanctions on 25 June EPA Tensions high as Trump approves new Iran sanctions: In pictures An Iranian navy boat tackles the fire on the Norwegian owned Front Altair oil tanker after it was hit in a suspected attack AFP/Getty Tensions high as Trump approves new Iran sanctions: In pictures Iran claims that in this picture released by Iran state TV, debris from the downed US drone is seen after it was recovered from Iranian waters AFP/Getty Tensions high as Trump approves new Iran sanctions: In pictures Smoke billows from an oil tanker after it was subject to a suspected attacked at the Gulf of Oman on June 13 Reuters Tensions high as Trump approves new Iran sanctions: In pictures A screenshot from a video released by the US Department of Defense that the US claims to show Iranian removing an unexploded limpet mine form the hull of the Japan-owned ship that was attacked in the Gulf of Oman on June 13 Getty Tensions high as Trump approves new Iran sanctions: In pictures An item reportedly found on the Japan-owned oil tanker that was attacked on June 13 in the Gulf of Oman AFP/Getty Tensions high as Trump approves new Iran sanctions: In pictures A handout photograph from the US Department of Defense shows a composite material that the US claim was left behind on the hull of the Japan-owned oil tanker following the removal of an unexploded limpet mine Getty Tensions high as Trump approves new Iran sanctions: In pictures A view from the cabin of an Iranian navy boat as it tackles the fire on the Norwegian owned Front Altair oil tanker after it was hit in a suspected attack EPA Tensions high as Trump approves new Iran sanctions: In pictures Release by US government A picture released by U.S. Central Command shows damage to the hull of the oil tanker Kokuka Courageous. The picture suggests that the ship is 'likely' to have been hit by a mine as the US Secretary of State Mike Pompeo moves to blame Iran for the suspected attack Reuters Tensions high as Trump approves new Iran sanctions: In pictures Smoke billows from an oil tanker after it was subject to a suspected attacked at the Gulf of Oman on June 13 Reuters Tensions high as Trump approves new Iran sanctions: In pictures Release by US government A picture released by U.S. Central Command shows damage to the hull of the oil tanker Kokuka Courageous. The pictures suggests that the ship is 'likely' to have been hit by a mine as the US Secretary of State Mike Pompeo moves to blame Iran for the suspected attack EPA

The Trump administration has long sought to base troops in the remote region, but the decision to send them to Saudi Arabia comes amid outrage over the killing of journalist Jamal Khashoggi. A United Nations report concluded his death at the Saudi embassy in Istanbul was "an extrajudicial execution" sanctioned Crown Prince Mohammed bin Salman.

The Trump administration has also been criticised for its response to the murder.

Despite these issues, the US has said it is committed to helping protect Saudi Arabia from Iranian aggression, and last month said 1,000 troops were being sent to the middle east, but did not say which countries they were going to.

Photographs taken by high-resolution commercial satellites, captured by satellite imagery company Planet Labs, show a deployment of US troops and support personnel who arrived at the air base in mid-June, according to Jeffrey Lewis, director of the East Asia Nonproliferation Project at the Middlebury Institute of International Studies at Monterey, who has studied the new images.

Pictures of the site taken in late June and early July show preparations being made for the arrival of troops, Mr Lewis told CNN.

“A small encampment and construction equipment appeared at the end of a runway by June 27, suggesting that improvements are already underway. The encampment to the east of the runway is typical of Air Force engineering squadrons deployed overseas,” he said.

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The US is reportedly hoping to be able to fly stealth, fifth-generation F-22 jets and other fighter planes from the base.

Commander Rebecca Rebarich, a Pentagon spokeswoman, told the New York Times there was “no official announcement” of the deployment to the Middle East but said the American military “continually works to manage our force posture in the region.”