U.S. President Donald Trump threw cold water Monday on Iran's denial of involvement in drone attacks carried out on key Saudi Arabian oil facilities.

"Remember when Iran shot down a drone, saying knowingly that it was in their 'airspace' when, in fact, it was nowhere close," Trump wrote on Twitter, referring to the downing of an American drone in June. "They stuck strongly to that story knowing that it was a very big lie. Now they say that they had nothing to do with the attack on Saudi Arabia. We’ll see?"

Yemen's Iran-backed Houthi rebels claimed responsibility on Sunday for the attack, and carried out the day prior on two Aramco facilities, warning foreign companies and workers against coming close to the company's sites which, they said, might "be targeted again".

Iran, however, has denied any role in the coordinated attacks on an oil field and the sprawling Abqaiq oil processing plant in eastern Saudi Arabia.

The incident prompted a spike in the price of brent crude, with prices up early Monday morning by nearly 10%.

Tensions have flared between Washington and Tehran since Trump chose in May 2018 to unilaterally remove the U.S. from a nuclear pact world powers struck with Iran that provided the Islamic Republic with billions of dollars in sanctions relief in exchange for unprecedented curbs on its nuclear program.

The Houthis, whose medium and long-range ballistic missiles are usually intercepted and neutralized by the Saudi air defense system, have repeatedly targeted strategic locations in Saudi Arabia with armed drones.

Yemen has remained wracked by violence since 2014, when the Iran-aligned Houthi group overran much of the country, including the capital Sanaa.

The conflict escalated the following year, when Saudi Arabia and its Arab allies launched a massive air campaign aimed at rolling back Houthi gains to support the country’s pro-Saudi government.

More than 70,000 people have been killed in the raging conflict since 2016, according to the UN estimates.