The U.N. Security Council scheduled a vote Friday on a resolution that would authorize U.N. monitors to observe the implementation of a cease-fire in Yemen's strategic port city of Hodeida and the withdrawal of rival forces — potential breakthroughs in the four-year civil war.

The U.N. envoy for Yemen, Martin Griffiths, called for urgent deployment of U.N. monitors as "an essential part of the confidence" needed to help implement the Dec. 13 cease-fire agreement between Yemen's government and Houthi Shiite rebels and the "phased but rapid mutual withdrawals" of fighters from the main port in Hodeida and two others in the province as well as from Hodeida city.

The fragile cease-fire has halted months of heavy fighting in Hodeida, through which the country imports 70 percent of its food and humanitarian aid. But the Saudi-led coalition backing the government bombed an air base in the rebel-held capital of Sanaa on Wednesday, and Yemeni officials have also reported sporadic artillery and automatic weapons fire.

After intense negotiations over the past week on a British-drafted resolution that would authorize U.N. monitors — including over whether to condemn Iran for supplying weapons to the Houthis which the U.S. wanted and Russia strongly opposed — the United States surprised the council by circulating a stripped-down rival resolution Thursday.

It is exceedingly rare for allies to present rival resolutions to the Security Council.

The British responded by putting their draft in a final form that can be voted on, and diplomats said it will be put to a vote on Friday morning.

If the British resolution doesn't get a minimum nine "yes" votes or is vetoed by another permanent member — the U.S., Russia, China or France — the United States could then seek a vote on its rival draft.

The British draft would authorize U.N. Secretary-General Antonio Guterres "to establish and deploy, for an initial period of 30 days ... an advance team to begin monitoring and to support and facilitate the immediate implementation of the Stockholm agreement."

It endorses the agreement and also requests Guterres to submit proposals "as soon as possible before Dec. 31" on how the U.N. will fully support the cease-fire, the redeployment of the rival forces from the Hodeida area. and other provisions in the accord.

In response to Russia's threatened veto of the resolution if a reference to Iran was kept in the resolution, the text now condemns "the supply, from whatever source, of weapons and associated material in contravention of the arms embargo" against the Houthis in 2015

The British draft also addresses the dire humanitarian situation in Yemen and backs Griffiths' efforts to facilitate "an inclusive political process."