President Donald Trump formally notified Congress that hostilities with Iran resumed earlier this month as U.S. forces carried out another round of strikes, sending oil prices higher and weighing on global markets.

Oil Climbs As Investors Weigh Geopolitical Risks

Late Monday, Dow futures fell 143.00 points, or 0.27%, to 52,621.00, while S&P 500 futures declined 11.00 points, or 0.15%, to 7,552.00 and Nasdaq 100 futures slipped 7.25 points, or 0.02%, to 29,468.50 as of around 8:35 p.m. EDT.

In commodities, WTI crude oil rose 2.21% to $79.87 per barrel, while Brent crude climbed 2.11% to $85.06 per barrel. Natural gas futures fell 0.28% to $2.889 per MMBtu.

Meanwhile, the U.S. dollar index, which tracks the greenback against a basket of currencies, stood at 101.245, down 0.03% on the day.

Asian markets were lower, with South Korea's KOSPI falling 0.99% to 6,739.81 and Japan's Nikkei 225 declining 0.70% to 66,774.82.

Trump Says Iran Conflict Has Entered A New Phase

Trump informed Congress that hostilities with Iran resumed on July 7, Reuters reported, citing a letter dated July 10.

He argued that the renewed conflict starts a fresh 60-day period under the War Powers Act during which his administration can continue military operations without additional congressional authorization.

In the letter, Trump said he had previously ordered a ceasefire that was later extended while the administration pursued a diplomatic resolution.

However, he accused Iran of violating a memorandum of understanding by attacking commercial vessels transiting the Strait of Hormuz, prompting the U.S. to resume military action.

"I directed this military action consistent with my responsibility to protect Americans and United States' national security and foreign policy interests," Trump wrote.

Congress previously passed a resolution urging Trump to withdraw U.S. forces from hostilities with Iran despite Republican majorities in both chambers.

CENTCOM Launches Third Night Of Iran Strikes

Meanwhile, in its latest post, U.S. Central Command said it began a third straight night of strikes against Iran at about 4:45 p.m. ET on Monday.

CENTCOM said the operations are aimed at imposing "a heavy cost" on Iranian forces and reducing their ability to attack commercial shipping and civilians in the Strait of Hormuz.