GENEVA, June 25 (Reuters) - Failure to renew a cross-border aid operation into Syria before it expires next month could trigger a new "humanitarian catastrophe" inrebel-held areas in the northwest, the World Health Organization said on Friday. Millions of people depend on the aid currently funnelled from Turkey straight into northwest Syria in an arrangement authorised by the U.N. Security Council. The WHO made its statement ahead of what is expected to be showdown next month between Western members of the Security Council who support renewing the crossing, and Russia which has blocked other cross-border operations before. read more Moscow, which has veto power on the Security Council and has backed Syrian President Bashar al-Assad"s fight against the rebels, has argued that aid can be delivered to northern Syria from the capital Damascus. "A large-scale U.N. cross-border response for an additional 12 months remains essential to save lives," WHO spokesman Christian Lindmeier told journalists in Geneva. "Failure to renew U.N. cross border authorisation would greatly diminish central humanitarian operations and plunge northwest Syria into yet another humanitarian catastrophe," he added. Around 1,000 trucks use the Bab al-Hawa crossing every month to deliver aid and medicines, including COVID-19 vaccines, to some 2.4 million people hemmed in along the Turkish border, according to U.N. agencies. "Cessation of these supplies can only lead to increases of illnesses and deaths," Lindmeier said. He said U.N. efforts to create a supply route from Damascus had not been successful and no such convoys had got through in the past 11 months. A resolution needs nine votes in favour 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 several resolutions related to Syria, often backed by China.