UNITED NATIONS (Reuters) - The United Nations has suggested that the Tal Abiyad border crossing between Syria and Turkey could be used to deliver aid to civilians in northeast Syria after Russia and China blocked the world body from using a crossing point on the Iraqi border to provide help.

Last month, the U.N. Security Council allowed a six-year-long cross-border aid operation to continue from two places in Turkey, but dropped crossing points from Iraq and Jordan due to opposition by Russia and China. Council approval was needed because the Syrian government did not consent.

The 15-member council also asked Secretary-General Antonio Guterres to report back this month on any possible alternative routes to the Al Yarubiyah crossing between Syria and Iraq to ensure aid deliveries. Western diplomats have said Al Yarubiyah's closure cuts off 40 percent of medical aid to northeastern Syria.

"If viable alternatives to Al Yarubiah are not found for medical items, the gap between the humanitarian response and humanitarian needs will increase," Guterres wrote in his report to the council, seen by Reuters on Saturday.

"From a security and logistical perspective, in the current context, the Tal Abiyad border crossing would constitute the most feasible alternative," he said.

The report said that in December 2019 there were 103 medical facilities being supported by aid groups across northeast Syria.

"These medical facilities received a significant amount of their medical supplies from the United Nations through Al Yarubiyah. At least 50 of these medical facilities ... were supported solely with medicines provided cross-border," it said.

Russian U.N. Ambassador Vassily Nebenzia last month dismissed concerns about closing the Iraq border crossing because he said the situation on the ground had changed and aid was being delivered to the northeast from within Syria.

Guterres' report said that the United Nations was able to transport 2.54 million medical treatments and 451 tonnes of medical equipment to northeast Syria from Damascus by air in 2019, but there were no road convoys with medical items.

"Air freight is significantly more expensive than road convoys," the report said, which also noted that Syrian government approval is needed for deliveries to the northeast and it "usually takes three to four months to respond."

Guterres noted in the report that "in the absence of consent from the Syrian Government or neighbouring countries to use border crossings into northeast Syria, the Security Council would need to authorize the United Nations and its implementing partners to use additional crossings."

Turkey has sent thousands of troops and equipment to northwest Syria, just south of its border, to head off a push in recent weeks by Russia-backed Syrian government forces to retake the rebel-held territory after nine years of war.