Meanwhile, U.S. stocks fell on Wednesday morning.

The S&P 500 fell 0.6%, the Nasdaq Composite tumbled 0.5% and the Dow Industrial Average fell 600 points.

The drop in stocks compounded a sell off already underway on Wall Street fueled by concerns about chip and tech stocks.

The Russell 2000 index, which track small and mid-cap companies, tumbled 0.7%.

Airline stocks were some of the hardest hit shares in pre-market trading Wednesday. Delta Air Lines and Southwest Airlines tumbled 3%, while United Airlines fell 3.5%. Other travel stocks, such as Carnival and Royal Caribbean Cruises fell around 2%.

Global stocks also sold off, with Spain’s flagship index falling more than 2%. Benchmark indexes in Germany, France, Italy and the U.K. were all down by around 1.5%.

On Tuesday, the U.S. said that Iran struck three commercial vessels near the Strait of Hormuz. Tehran has not claimed responsibility for the attacks.

Later in the day, the U.S. Treasury revoked a sanctions waiver that allowed Iranian oil to be sold into the global market and U.S. Central Command launched “a series of powerful strikes against Iran” in retaliation for the vessel attacks.

“Renewed tensions in the Middle East have interrupted what had become an increasingly complacent market narrative, prompting investors to reassess geopolitical risks after several weeks of pricing in a smooth path toward de-escalation,” said Capital.com market analyst Daniela Hathorn in a Wednesday morning note.

“The latest attacks have lifted oil prices, weighed on equity markets and reminded investors that while a ceasefire remains in place, a lasting agreement between the US and Iran is far from guaranteed,” she added.

After the U.S. and Iran signed a memorandum of understanding in mid-June, U.S. oil prices stabilized around $69-$70 per barrel and remained there for the better part of three weeks.

“For markets and the global economy, the prospect of a swift return to pre-conflict energy and goods flows through the waterway is fading,” said Geoff Yu, senior market strategist at BNY.