DUBAI, United Arab Emirates (AP) — The United States is “reinstating” a blockade on Iran in the Strait of Hormuz and will charge ships for safe passage, after another heavy exchange of fire threatened negotiations aimed at ending the war.

President Donald Trump said on social media Monday that Iranian ships will no longer be able to travel through the strait and America would charge a 20% toll on eligible cargo, as the conflict with Iran has intensified after peace talks failed to deliver meaningful progress.

“We are reinstating the THE IRANIAN BLOCKADE, so named because it is only stopping Iran’s ships or customers from entering or leaving,” Trump said online. “All other countries will have fair and open use of the Strait.”

The president said the toll would help cover “any and all costs necessary to do the job of providing safety and security to this very volatile section of the World.”

A fifth of the world’s oil and gas passed through the strait before Iran asserted control over it after the start of the war.

The latest exchange of fire was sparked by an Iranian attack on a container ship on Sunday in the Strait of Hormuz. Iran has asserted control over the critical waterway for international oil and gas since the United States and Israel started the war on Feb. 28.

Iran says it has the right to manage traffic through the strait and potentially charge fees in accordance with an interim peace deal reached last month. The U.S. and others dispute that, citing international law on freedom of navigation, and the American military has tried to establish an alternative route outside of Iranian control.

Iran and the U.S. are nearly halfway through the 60-day period in which they were supposed to negotiate a permanent end to the war and an agreement on Iran’s disputed nuclear program. Instead, a series of attacks over the strait have raised fears of a return to all-out war and further disruption to the global economy.

Oil prices jumped nearly 5% on Monday in early trading. U.S. benchmark crude, which had risen to nearly $120 a barrel at the height of the war, was trading at around $72.92. Markets overall were mixed.

US says it has struck dozens of targets in Iran

The U.S. military said it struck dozens of sites in the strikes Monday, including air defense systems, radar sites, missile and drone equipment, and small boats. It said Iran does not control the Strait of Hormuz.

The European Union’s top diplomat, Kaja Kallas, called for the strait to be open, as it was before the war. “Freedom of navigation has to be respected,” she said.