U.N. Ambassador Kelly Craft is warning of “mass graves” if the United Nations Security Council fails to extend a vital Syrian cross-border aid program, as she races against the clock to overcome Russian opposition. The program is due to expire in just over a week.

“What we’re really focused on in the Council is the outcome, and that is saving lives, that’s reaching over 4 million Syrians. And if we don’t, the COVID outbreak is going to … I hate to say this ... it’s going to be mass graves of very innocent people,” Craft told Fox News in an interview Wednesday.

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The cross-border aid program allows aid to be funneled into Syria by keeping open crossings on the borders in the north of the war-torn country. The years-long program was partially extended in January when Russia vetoed a resolution that would see four crossings open, and instead forced the Council to pass Resolution 2504, which reduced the border crossings to two and cut the mandate to six months.

That resolution runs out on July 10, and a resolution the U.S. supports would extend the opening of those two crossings – Bab al-Salam and Bab al-Hawa – in the rebel-held northwest on the border with Turkey by 12 months, and reopen the third Al Yarubiyah crossing in the northeast on the border with Iraq for an initial and renewable six-month period.

Although often isolated at the U.N., this is one area where the U.S. is in the majority. U.N. Secretary-General Antonio Guterres has called for the aid program to be extended, and the U.S. has the support of its allies on the Council. It’s also supported by the assessment of U.N. experts.

Undersecretary-General for Humanitarian Affairs Mark Lowcock told the Council this week that the northwest of Syria is suffering from a “major humanitarian crisis,” particularly with the COVID-19 outbreak, and called for the cross-border operation to be scaled up.

He warned that children and infants are arriving at nutrition centers with acute and chronic malnutrition, and that parents have had to resort to cooking weeds in order to supplement the scarce food rations to feed their children.

“A failure to extend the cross-border authorization would sever the UN operation currently underway,” Lowcock said. “It would end the UN food deliveries and the support to nutrition centres.”

“It would cause suffering and death.”

Craft told Fox News that extending the crossings to three is also vital: “It’s the only way….we’re going to be able to reach the northeast, that’s about 1.3 million people who are waiting on medical supplies.”

But Russia holds veto power at the Council, and opposes the expansion of crossings. Moscow, which supports the brutal regime of Syrian President Bashar al-Assad, has claimed that the cross-border aid was only a temporary fix and has instead become a political tool to stoke division in Syria.

Russia has long been a thorn in the side for multiple U.S. ambassadors, and Craft is trying to find a way to overcome the Russian obstinance. Meanwhile, Ambassador James Jeffrey, the special representative for Syria engagement, has been in Vienna to take part in U.N. negotiations there to try and break the impasse.

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“The main opposition is as it was, in January, it’s Russia, and China will pretty much vote the way of Russia, so my main goal is to keep the lines of communication open with the Russian [permanent representative]," Craft told Fox News.

The Russian ambassador, Vassily Nebenzia, is particularly prickly and regularly engages in anti-U.S. rants at the Security Council table. But Craft says they have developed a good working relationship and says she intends to keep trying to find a solution until the day of the vote -- expected to be July 10.

Craft had visited the refugee camps in March and on Wednesday spoke about her fears that the COVID outbreak could be disastrous at camps with bare necessities and where refugees are tightly packed in.

“To see the passion in the eyes of the refugees and how they look to America -- we have a moral responsibility, I take that very seriously,” she said.

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She also had harsh words for the Assad regime, and those countries propping it up.

“Assad does not care about his people, his is a rogue regime,” she said. “We care deeply, American taxpayer dollars are being used to save lives and we want to make certain we have full accessibility to as many lives as we possibly can to save.”

But in the face of so far unyielding opposition from the Russians, Craft said that the U.S. and groups like the World Food Program and UNICEF intend to be ready and prepared both for the program to be opened or closed.

"I wish I sounded more optimistic, I want to be cheerfully optimistic, but at the same time I have to think about these lives and that just keeps me moving forward," she said.

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She also acknowledged the pressure being put on Russia by a growing consensus at Turtle Bay and elsewhere that the Russians should back down and allow the program to be extended.

“I think what that does mean is it’s going to put pressure on them, and whatever the outcome is going to be, someone is going to be responsible for the lives,” she said. "If we lose lives, they will be held responsible.”

The Associated Press contributed to this report.