Despite objections by Syria’s government, the United Nations Security Council voted 15 to 0 on Monday to authorize cross-border convoys of emergency aid for millions of deprived Syrian civilians in rebel-held areas, without prior approval by the Syrian authorities.

Monday’s resolution strengthened the provisions of another adopted five months ago and signified a rare unanimity among the Security Council members over how to deal with the civil war in Syria, which is now in its fourth year. The conflict has left more than 150,000 people dead, spread instability in the region and created what international aid officials are calling one of the world’s biggest humanitarian disasters.

Nearly half of Syria’s population — 10.8 million people — need assistance because of the war, and roughly half of them live in rebel-held areas.

The resolution was the Council’s response to the repeated frustrations of relief officials from the United Nations and other emergency relief groups over their inability to reach these civilians, who are trapped in besieged areas or otherwise hard-to-reach parts of the country because of the fighting. The Security Council resolution on Syria passed in February, aimed at allowing the widespread distribution of aid, has been repeatedly subverted or ignored.