WASHINGTON/RIYADH, June 24 (Reuters) – U.S. President Donald Trump imposed new U.S. sanctions on Iran on Monday following Tehran’s downing of an unmanned American drone and said the measures would target Iranian Supreme Leader Ayatollah Ali Khamenei.

Trump told reporters he was signing an executive order for the sanctions amid tensions between the United States and Iran that have grown since May, when Washington ordered all countries to halt imports of Iranian oil.

Trump also said the sanctions would have been imposed regardless of the incident over the drone. He said the supreme leaders was ultimately responsible for what Trump called “the hostile conduct of the regime.” “Sanctions imposed through the executive order … will deny the Supreme Leader and the Supreme Leader’s office, and those closely affiliated with him and the office, access to key financial resources and support,” Trump said.

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The Trump administration wants to force Tehran to open talks on its nuclear and missile programs and its activities in the region.

Iran said on Monday U.S. cyber attacks on its military had failed, as Washington sought to rally support in the Middle East and Europe for a hardline stance that has brought it to the verge of conflict with its longtime foe.

Washington has blamed Tehran for attacks on tankers in the Gulf in recent weeks, which Iran denies. On Monday, the United States said it was building a coalition with allies to protect Gulf shipping lanes.

WATCH: Trump announces ‘hard-hitting’ U.S. sanctions on Iran

7:12 Trump announces new U.S. sanctions on Iran targeted at supreme leader Trump announces new U.S. sanctions on Iran targeted at supreme leader

A coalition of nations would provide both material and financial contributions to the program, a senior U.S. State Department official said, without identifying the countries.

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“It’s about proactive deterrence, because the Iranians just want to go out and do what they want to do and say hey we didn’t do it. We know what they’ve done,” the official told reporters, adding that the deterrents would include cameras, binoculars and ships.

The United States accuses Iran of encouraging allies in Yemen to attack Saudi targets.

In a joint statement on Monday, the United States, Saudi Arabia, the UAE and Britain expressed concern over Middle East tensions and the dangers posed by Iranian “destabilizing activity” to peace and security in Yemen and the region.

READ MORE: Mike Pompeo says he discussed Gulf maritime security with Saudi king