The 15-member Security Council on January 10 voted to allow cross-border deliveries to continue from two sites in Turkey, but it eliminated crossing points from Iraq and Jordan.
The effort was also renewed for only six months instead of the usual one year.
The UN and aid groups have since 2014 crossed into Syria from Turkey, Iraq, and Jordan at four places in a program authorized annually by the Security Council.
Russia and China abstained from the vote.
The United States and Britain also abstained, expressing anger over the reduced scale of the operation, which had been scheduled to expire at the end of the day on January 10. The 11 other Council members voted for the extension.
The UN estimated that 2.7 million people in northwestern Syria and 1.3 million in the northeast relied on assistance from the cross-border operations. The Syrian government has not consented to the deliveries.
Syrian government forces have launched an offensive in northwest Idlib Province, the last stronghold of antigovernment forces and extremist fighters mixed among some 3 million civilians.
The UN has warned of the heightening risk of a humanitarian disaster along the Turkish border.
Karen Pierce, Britain’s UN ambassador, accused Russia of politicizing the issue and said before the vote that authorizing only two crossing points for six months was “an inadequate response to the situation on the ground.”
“There are some 1.8 million people at risk in the northeast if we don’t find a way to help them. This is winter. One can imagine how dire the situation becomes,” Pierce told reporters.
Russian UN Ambassador Vassily Nebenzia rejected her comments, saying the situation had changed dramatically and that Security Council action should reflect that.
“All these cries about imminent catastrophe, disaster, which northeast faces if we close one cross-border point is totally irrelevant because humanitarian assistance to that region is coming from within Syria,” he told reporters ahead of the vote.
The UN has said it has no alternative to the cross-border operation, but Nebenzia said “alternatives exist” because the area is largely controlled by the Syrian government, a close ally of Russia.
Moscow argues that aid is being delivered at a sufficent level by the Syrian government.
Russia and China last month vetoed a draft resolution that would have authorized three crossing points for one year. It was Russia’s 14th UN Security Council veto since the start of the Syrian conflict.
U.S. Secretary of State Mike Pompeo called the veto as “shameful” and told Moscow and Beijing that “you have blood on your hands.”
Russia, along with Iran, has provided crucial support for the government of Syrian President Bashar al-Assad in the country’s civil war, which broke out after a government crackdown on protesters in March 2011.
The United States and Turkey support differing rebel groups in Syria, while terror groups, including those linked to Islamic State and Al-Qaeda, have become involved in the fighting, which has killed more than 400,000 people and displaced million since the start of the war.