US.Ambassador to the United Nations Kelly Craft urged her Security Council counterparts on Wednesday to oppose a Russian bid to cut border access for aid deliveries to millions of Syrian civilians, describing the choice as "good versus evil."

Russia and China cast vetoes on Tuesday to block the 15-member council from extending its approval for a year of aid deliveries to Syria from Turkey through two border crossings. Russia then put forward its own text that would only approve one of those crossings for aid access for six months.

"This is a good versus evil, this is a right versus wrong and it is the right thing to do to vote against the Russian text," Craft told Reuters. "It is the right thing to do to really work toward having the two border crossings remain open."

"We're talking about the difference between life and death for millions of Syrians," she said.

Russia and China have argued that cross-border aid deliveries are not needed as those areas can be accessed from within Syria.

The more than six-year long cross-border aid operation is currently authorized until Friday, so if the Russian resolution fails to pass another council member could put forward a new proposal for a vote. A resolution needs nine votes in favor and no vetoes by Russia, China, the United States, France or Britain.

During the coronavirus pandemic the council has been operating virtually, which means members have 24 hours to cast a vote on a draft resolution. The result of the vote on the Russian text will be announced later on Wednesday.

Craft said she had been lobbying her council counterparts - all of whom voted in favor of the draft resolution vetoed by Russia and China on Tuesday - as had Russia and China.

Craft accused Russia and China of wanting to end all cross-border humanitarian assistance for Syria in an effort to help "prop-up" Syrian President Bashar al-Assad's government.

A crackdown by Syrian Assad on pro-democracy protesters in 2011 led to civil war, with Moscow backing Assad and Washington supporting the opposition. Millions of people have fled Syria and millions are internally displaced.