WASHINGTON (AP) — President Donald Trump signed an executive order on Monday targeting Iran's supreme leader and his associates with financial sanctions, the latest action the U.S. has taken to discourage Tehran from developing nuclear weapons and supporting militant groups.

The sanctions follow Iran's downing of a more than $100 million U.S. surveillance drone over the Strait of Hormuz that has ratcheted up tensions. Trump pulled back from the brink of retaliatory military strikes on Iran last week, but is continuing his pressure campaign.

The targets of the new sanctions include senior military figures in Iran, blocking their access to any financial assets under U.S. jurisdiction.

"These measures represent a strong and proportionate response to Iran's increasingly provocative actions," Trump told reporters in the Oval Office.

"We will continue to increase pressure on Tehran until the regime abandons its dangerous activities and its aspirations, including the pursuit of nuclear weapons, increased enrichment of uranium, development of ballistic missiles, engagement and support for terrorism, fueling of foreign conflicts and belligerent acts directed against the United States and its allies."

The sanctions work to deny Supreme Leader Ali Khamenei and his close aides access to money and support.

Iran's naval commander, however, has warned that Iranian forces would not hesitate to act again and shoot down more U.S. surveillance drones that violate Iranian airspace. The U.S. said the drone was flying over international waters.

"We confidently say that the crushing response can always be repeated, and the enemy knows it," Rear Adm. Hossein Khanzadi was quoted as saying by the semi-official Tasnim news agency.

Tensions have been escalating since Trump last year withdrew the U.S. from a global nuclear deal with Iran and re-imposed economic sanctions on Iran.

Iran has decried the U.S. sanctions, which essentially bar Iran from selling its oil internationally, as "economic terrorism."

Earlier, Trump suggested that the United States should not protect ships in the strategic Strait of Hormuz without compensation from other countries.

The U.S. blamed Iran for attacks on two oil tankers this month near the strait, denouncing what it called a campaign of "escalating tensions" in a region crucial to global energy supplies.