(CNN)--Global oil prices surged sharply Tuesday following the collapse of the ceasefire between the United States and Iran, and threats by the US military to resume its naval blockade of Iranian ports.

Brent crude, the global benchmark, reached $87 per barrel before the opening of US markets, its highest level since June 12. At the same time, West Texas Intermediate crude, the US benchmark, rose 3.6% to near $81 per barrel.

The status of the vital Strait of Hormuz, through which a fifth of the world's oil passed before the war, has become uncertain again. Tehran announced the "closure" of the waterway over the weekend, and President Donald Trump stated that the United States would become the "protector" of the strait and would impose a 20% fee on commercial shipping companies based on the value of their cargo in exchange for Washington's protection.

The US Central Command announced Monday that it intends to resume the naval blockade on ships entering and leaving Iranian ports as of 4:00 PM Eastern Time Tuesday. The United States had imposed a blockade for nearly two months starting in mid-April, which contributed to a significant rise in oil prices.

US stock futures pointed to a mixed opening, with the Dow Jones down 0.2%, the S&P 500 down 0.1%, while the tech-heavy Nasdaq rose 0.4%.

European stock markets were trading lower in early afternoon local time. The Stoxx Europe 600, the region's main index, fell 0.5%, while Germany's DAX dropped 0.5% and France's CAC fell 0.7%. Asian markets, for their part, mostly ended Tuesday's session higher.