Russia, supported by China, has shielded its ally Syria on the Security Council during the three-year-long war. They had previously vetoed three resolutions that would have condemned Syria's government and threatened it with possible sanctions.
Lithuanian UN Ambassador Raimonda Murmokaite, president of the 15-member council for February, described the unanimous approval of the resolution, drafted by Australia, Jordan and Luxembourg, as a "moment of hope" for Syria's people.
Russia's UN Ambassador Vitaly Churkin told the council after the vote that Moscow supported the move because "many Russian considerations were borne in mind and as a result the document took on a balanced nature."
China's UN Ambassador Liu Jieyi said that Beijing was "gravely concerned" by Syria's worsening humanitarian situation. "We strongly urge all the parties in Syria to implement this resolution in good faith," he said.
The initial text was weakened during negotiations with references to the International Criminal Court and targeted sanctions removed. But other contentious points including a demand for an end to barrel bombs, a demand for cross-border access and the naming of besieged areas were included.
"This resolution goes further than we have been able to get in three years," US Ambassador Samantha Power told reporters. "But a resolution is just words, it is implementation that matters and that's what we're starting measuring right now."
The resolution asks UN Secretary-General Ban Ki-moon to report to the council in 30 days on implementation and "expresses its intent to take further steps in the case of non-compliance." Diplomats say Russia is unlikely to agree to any action if Syria's government was found to be in non-compliance.
But several Western envoys expressed a strong intent to push for Security Council action if the resolution is ignored.
"Of course we would have liked to have seen this resolution be even stronger than it is but we are committed to coming back to the council to seek further action if the demands are not met," British Ambassador Mark Lyall Grant told reporters.
Australian UN Ambassador Gary Quinlan said the Syrian conflict was "the biggest and the most devastating humanitarian crisis we're currently facing." He said: "There will be consequences for non-compliance. We will remain determined."
Russian Foreign Ministry spokesman Alexander Lukashevich said in a statement on Saturday that the resolution "contains no threat of enforcement by sanctions."
The United Nations says 9.3 million people need help - nearly half the population - and that well over 100,000 people have been killed. The opposition Syrian Observatory for Human Rights has said that more than 136,000 have been killed since a revolt against President Bashar Assad began in March 2011.
"This resolution should not have been necessary. Humanitarian assistance is not something to be negotiated; it is something to be allowed by virtue of international law," Ban told the council after the vote. "Profoundly shocking to me is that both sides are besieging civilians as a tactic of war," the UN Secretary-General added.
The resolution "demands that all parties, in particular the Syrian authorities, promptly allow rapid, safe and unhindered humanitarian access for UN humanitarian agencies ... including across conflict lines and across borders."
It also demands all parties "cease all attacks against civilians, as well as the indiscriminate employment of weapons in populated areas, including shelling and aerial bombardment, such as the use of barrel bombs, and methods of warfare ... to cause superfluous injury or unnecessary suffering."
Syria's UN Ambassador Bashar Ja'afari said the Damascus government "has continued to work day and night in order to fulfill all of the humanitarian needs of its citizens."
"The Syrian government bears the largest share of the humanitarian assistance distributed in Syria, it has covered 75 percent of this assistance, whereas U.N. organizations and other international organization operating in Syria have covered only 25 percent," Ja'afari told the council.
Najib Ghadbian, the opposition Syrian Coalition special representative to the United Nations, described the resolution as "a modest but necessary first step towards addressing the dire humanitarian needs of the Syrian people."
"But at this point, it is only a text. It is crucial that the resolution is implemented immediately and in full," he said in a statement.
The resolution strongly condemned "the increased terrorist attacks resulting in numerous casualties and destruction carried out by organizations and individuals associated with al-Qaeda , its affiliates and other terrorist groups."
Russian's Churkin called on opposition groups in Syria to support the Syrian government in the fight against terrorism.
"We consider that the Security Council should swiftly move on to discussing a separate draft document to counter terrorist activity in Syria," the ambassador told the council.
The Security Council has now adopted five resolutions linked to the Syrian conflict. Aside from the aid access resolution, three resolutions were adopted in 2012 to mandate a failed UN observer mission to Syria and one last year on eradication of Syria's chemical weapons.
Western members of the Security Council have been considering a humanitarian resolution for almost a year. After months of talks, the council adopted a non-binding statement on Oct. 2 urging more access to aid, but that statement produced only a little administrative progress.
UN aid chief Valerie Amos had urged the Security Council to act to increase humanitarian access in Syria. Amos has repeatedly expressed frustration that violence and red tape have slowed aid deliveries to a trickle.
"I hope that the passing, by the United Nations Security Council, of a humanitarian resolution will facilitate the delivery of aid to people in desperate need in Syria," Amos said in a statement after the vote.