US President Donald Trump has signed an executive order that would impose new sanctions on Iran, amid increased tension between the long-time foes.

Mr Trump initially told reporters the sanctions, which will target Iranian Supreme Leader Ayatollah Ali Khamenei and his office, were in response to the Iranian downing of a US drone last week.

Iran has said the drone was flying in its airspace, which the US has denied.

Later, Mr Trump said the sanctions would have been imposed regardless of the incident over the drone.

The US has also blamed Iran for attacks earlier this month on two oil tankers at the entrance of the Gulf of Oman. Iran, in turn, has denied that it is to blame.

The US has repeatedly imposed sanctions on Iran since last year, when it withdrew from a 2015 deal that had seen Iran curb its nuclear programme in exchange for easing of sanctions.

Mr Trump's administration has said the deal struck under his predecessor Barack Obama did not do enough.

The Republican has said he would be open to talks with Iranian leaders, but Iran has rejected such an offer unless Washington drops the sanctions.

Footage on drone wreckage shown on Iranian TV last week

Meanwhile, US Secretary of State Mike Pompeo discussed Iran and maritime security with rich Gulf Arab allies during a trip to the region.

The visit comes after Mr Trump called off a military strike to retaliate for the drone incident

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A senior US State Department official said that the US is building a coalition with its allies to protect Gulf shipping lanes by having "eyes on all shipping", following the recent incidents in the Gulf.

Mr Pompeo arrived in the United Arab Emirates after meeting King Salman and Crown Prince Mohammed bin Salman in Saudi Arabia where talks covered protection for ships.

"Freedom of navigation is paramount," Mr Pompeo tweeted from the Saudi city of Jeddah.

The senior US official told reporters en route to Abu Dhabi that Mr Pompeo and the US Navy is building a "Sentinel" programme for "proactive deterrence".

He said a coalition of nations would provide both material and financial contributions, but did not name the countries.

"What the Iranians are doing by shooting down American drones, shooting at other drones in the region not even necessarily over the Gulf, anywhere, is to prevent us from having eyes on them," the official said.

Iran has denied any involvement in the explosive blasts that have hit six vessels, including two Saudi oil tankers, near the Strait of Hormuz, through which almost a fifth of the world's oil passes.

The US official said the deterrents include cameras, binoculars and ships, including from the US.