UNITED NATIONS, June 23 (Reuters) - U.N. Secretary-General Antonio Guterres appealed to the Security Council on Wednesday to renew a cross-border aid operation into war-torn Syria for another year, warning that a failure to do so would be devastating for millions of people. Guterres addressed the 15-member body ahead of a likely showdown next month between Western members and Russia and China over the renewal of the mandate for the long-running aid operation, which expires on July 10. "A failure to extend the council"s authorization would have devastating consequences," Guterres said. The 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 that leads into a rebel-held area in northwestern Syria due to opposition from Russia and China over renewing all four. Council veto-power Russia - an ally of Syrian President Bashar al-Assad - has questioned the importance of the cross-border aid operation, arguing that aid can be delivered to northern Syria from the capital Damascus. Russia"s U.N. Ambassador Vassily Nebenzia told the council the aid operation violated Syria"s sovereignty and territorial integrity and Moscow only agreed to the operation in 2014 because the Syria was being "riven into parts by terrorists." He said now most of Syria"s territory had been "liberated" the cross-border aid operation "is simply an anachronism." Syrian U.N. Ambassador Bassam Sabbagh rejected the cross-border aid operation as politicized and said it was "a temporary exceptional measure - the reasons and conditions that led to its adoption no longer exist." In a swipe at the United States and others, both Russia and China blamed unilateral sanctions for some of Syria"s plight. U.S. Ambassador to the United Nations, Linda Thomas-Greenfield, rejected that argument: "Serious economic woes are the result of the Assad regime"s gross corruption and mismanagement of the Syrian economy." The United Nations and aid groups have warned there is no substitute for the delivery of cross-border aid into Syria. "Without cross-border access, more Syrians will die," Thomas-Greenfield, who visited the Turkish border crossing being used to deliver aid three weeks ago, told the council. Ireland and Norway plan to circulate a draft resolution in the coming days to "renew and expand the humanitarian aid delivery mechanism in response to the pressing humanitarian needs," Ireland"s U.N. Ambassador Geraldine Byrne Nason said. A resolution needs nine votes in favor and no veto from any of the five permanent members Russia, China, the United States, France and Britain. In the past decade, the council has been divided on Syria - Russia has vetoed 16 resolutions related to Syria and was backed by China for many of those votes. Reporting by Michelle Nichols