Yemen announced on Monday it was imposing a naval blockade on Saudi Arabia, a move that opens a new front against the United States in its war on Iran and widens the threat to global oil supplies and trade beyond the Persian Gulf.

In the statement, Yemen’s armed forces said they were declaring “a maritime embargo against the criminal Saudi enemy, based on the equation of ‘an eye for an eye’, effective immediately...”

They said the decision was in response to “an unjust and oppressive siege” imposed on Yemen by the Saudis, NBC News reported.

There was no immediate response from Saudi Arabia.

The full closure of the Bab el-Mandeb strait would reduce global oil supply by 7% as it would leave most of Saudi oil exports unable to leave the region. The disruption would add to the massive cut to global oil flows from the war in the Persian Gulf, which has already reduced shipments by 10% of global supply.

The announcement followed signs from both Iran and the U.S. that they wanted to resume diplomatic efforts to end an escalating cycle of attacks that has all but wrecked a fragile interim agreement signed last month.

A senior Iranian official told Reuters on Monday that Tehran had received a proposal from mediators for a 10-day ceasefire in an effort to salvage the interim deal, intended to pave the way to a lasting agreement to the war that began on February 28 with U.S.-Israeli attacks on Iran.

Oil prices briefly jumped above $90 a barrel earlier on Monday after renewed disruption to shipping through the Strait of Hormuz. They later pared gains after Iran’s Foreign Ministry said mediators had recently presented proposals to Tehran, signaling that diplomatic contacts remain active.

Neither the ministry nor the official who spoke to Reuters gave any further details on the putative ceasefire discussions.

Iran’s Interior Minister, Eskandar Momeni, was making a second visit to Islamabad in less than a week.

A 14-point memorandum of understanding (MOU) that was signed between Iran and the U.S. on June 18 with Pakistan’s mediation was aimed at finding a lasting solution to the conflict between Iran and the U.S. and reopening the Strait of Hormuz.