The United States and Iran each asserted Monday they controlled the Strait of Hormuz after a weekend of attacks stretching across the wider Middle East, further threatening any diplomacy to end the war.

The latest exchange was sparked by an Iranian attack on a container ship on Sunday in the Strait of Hormuz, a critical waterway for international oil and gas over which Iran has asserted control 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. disputes that, citing international law on freedom of navigation, and 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.

“A return to full-scale hostilities would have catastrophic consequences,” United Nations Secretary-General António Guterres said in a statement.