Iranian-aligned Houthi forces have agreed to draw back from two Yemeni ports on Monday while withdrawal from the main Hodeidah port will occur later alongside a retreat by coalition-backed forces massed outside the city, U.N. and Yemeni sources said.

Houthi forces will withdraw 5 km (3 miles) from the ports of Saleef, used for grain, and Ras Isa, an oil terminal, as a first step agreed with the internationally recognized government, three sources said.

The Houthi withdrawal from Hodeidah port and the pull-back by coalition forces 1 km away from the city’s “Kilo 7” eastern suburb would take place as a second step, they said.

An orderly troop withdrawal from Hodeidah, now a focus of an almost four-year war, is key to U.N.-led efforts to avert a full-scale assault on the port and pave the way for political negotiations.

The conflict has killed tens of thousands of people and pushed Yemen to the brink of famine.

The United Nations has been trying to salvage a truce deal agreed at peace talks in December between the Houthis and the Saudi-backed government. That process has stalled over who would control of Hodeidah, a Red Sea port used to feed Yemen’s 30 million people.

Hodeidah is held by the Houthis while other Yemeni forces backed by the Saudi-led coalition loyal to ousted President Abd-Rabbu Mansour Hadi are positioned on the edges of the city.

Hadi’s top negotiator, Foreign Minister Khalid al-Yamani, said the initial Houthi redeployment must be verified before further progress can be made and humanitarian corridors reopened.

“This is what was agreed by the Yemeni government: we verify the first step before implementing the second,” he told Asharq al-Awsat newspaper in remarks published on Sunday.

A small team of U.N. observers arrived in Hodeidah after the ceasefire went into effect on Dec. 18 to oversee troop redeployments by both sides.

The deal calls for local authorities to assume control of Hodeidah but did not detail the process, leaving it open to interpretation.

The Western-backed Sunni Muslim coalition led by Saudi Arabia and the United Arab Emirates intervened in Yemen in 2015 to try to restore Hadi’s government after it was ousted from power in the capital Sanaa in late 2014.

The conflict, widely seen in the region as a proxy war between Saudi Arabia and Iran, has been locked in military stalemate.

The Houthis, who say their revolution is against corruption, control most urban centers including Sanaa. Hadi’s government holds the southern port of Aden and a string of coastal towns.