ADEN (Reuters) - The five permanent members of the U.N. Security Council urged Yemen’s warring parties on Tuesday to implement a peace deal in the port city of Hodeidah, a move they hope will lead to an end of the four-year-old conflict.

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The Chinese, French, Russian, British and U.S. ambassadors to Yemen said in a statement they were “extremely concerned” that the agreement reached in Stockholm in December had not been implemented.

The Houthi group and the Saudi-backed government agreed on a ceasefire and troop withdrawal in Hodeidah, an exchange of prisoners, and the reopening of humanitarian corridors to help millions of starving Yemenis, with international monitors to oversee things.

“We ... urge both parties to begin implementation of the proposal in good faith without further delay and without seeking to exploit the redeployments by the other side,” they said.

“We call on all sides to ensure the U.N. monitoring mission can carry out its work safely and without interference.”

The Stockholm agreement stalled with each side worrying the other would take advantage of the withdrawal to gain ground.

The formation of a local authority to take control of Hodeidah after the troop withdrawal, agreed in the truce deal, also remains a sticking point.

The truce in Hodeidah came into force on Dec. 18 and has largely held but violence has escalated in other regions.

Air strikes by the Saudi-led coalition killed at least 22 civilians, including women and children, in a village in northern Yemen this week, the United Nations said.

Saudi Arabia is leading the Western-backed Sunni Muslim coalition that first intervened in Yemen in 2015 to try to restore Abd-Rabbu Mansour Hadi’s ousted government.

Western nations have pressed for an end to the war following increased scrutiny after the murder of prominent Saudi journalist Jamal Khashoggi.

The conflict is widely seen as a proxy war between Saudi Arabia and Iran. The Houthis deny receiving help from Tehran and say their revolution is against corruption.