US ambassador to the United Nations, Linda Thomas-Greenfield speaks during a press conference for the Security Council programme of work in March at the UN Headquarters in New York on March 1, 2021. (TIMOTHY A. CLARY / AFP)

US Ambassador to the United Nations, Linda Thomas-Greenfield, will visit the Turkish border with Syria this week ahead of a likely showdown with Russia in the UN Security Council over the extension of a cross-border humanitarian aid operation.

Thomas-Greenfield will visit Turkey from Wednesday to Friday, meeting with senior Turkish officials, UN agencies, aid groups and Syrian refugees, senior officials with the US mission to the United Nations said on Tuesday.

Thomas-Greenfield will "convey the United States' strong support for humanitarian access into Syria and the US commitment to the people of Syria," said one US official.

US Ambassador to the United Nations, Linda Thomas-Greenfield, will visit Turkey from Wednesday to Friday, meeting with senior Turkish officials, UN agencies, aid groups and Syrian refugees, senior officials with the US mission to the United Nations said on Tuesday

"Nothing could be more urgent than continuing to provide life-saving aid through the cross-border mechanism ... This has grown even more significant and more dire," the US official said.

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The 15-member Security Council first authorized a cross-border aid operation into Syria in 2014 at four points. Last year, it reduced that access to one crossing point from Turkey due to opposition from Russia and China over renewing all four.

Another showdown is likely over the renewal of the mandate for the operation, which expires on July 10. A resolution to extend council approval needs nine votes in favor and no veto from any of the five permanent members Russia, China, the United States, France and Britain.

Several council members, including the United States, are pushing to expand the cross-border operation.

"Nothing else can deliver the amount of aid in the frequency needed to support vulnerable populations in northern Syria," said the US official.

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UN aid chief Mark Lowcock appealed to the Security Council last week not to cut a cross-border aid "lifeline" to some 3 million Syrians in the country's north as Russia questioned the importance of the operation.