The 15-member council voted on two rival drafts, one humanitarian-focused resolution proposed by Germany, Belgium and Kuwait and backed by the US, the other a text by Russia and China.
Permanent Security Council members Russia and China vetoed the first draft resolution because it did not include language that would exempt from the truce military offensives against what they called "terrorists."
Russian Ambassador Vassily Nebenzia argued that the text's real purpose was to "save international terrorists entrenched in Idlib from their final defeat."
German Ambassador Christoph Heusgen said he was "deeply disappointed" by the outcome of the vote.
"This council will not be able to fulfil its duty to protect the lives of 3 million people, mainly women and children, in Idlib governate," he said.
Syrian forces, bolstered by Russian air power, began bombing the country's north-west region, including the mainly rebel-held province of Idlib, at the end of April.
A senior UN official told the Security Council on Thursday that an estimated 400,000 people have fled their homes in Syria's north-west in the last four months.
Moscow's veto was not a surprise. It has vetoed around 13 draft Security Council resolutions on Syria over the eight years of war to protect its ally, Syrian President Bashar al-Assad.
The rival draft resolution, tabled by Moscow and Beijing on Wednesday without prior discussions with other council members, was also voted down.
Permanent Security Council members Russia and China vetoed the first draft resolution because it did not include language that would exempt from the truce military offensives against what they called "terrorists."
Russian Ambassador Vassily Nebenzia argued that the text's real purpose was to "save international terrorists entrenched in Idlib from their final defeat."
German Ambassador Christoph Heusgen said he was "deeply disappointed" by the outcome of the vote.
"This council will not be able to fulfil its duty to protect the lives of 3 million people, mainly women and children, in Idlib governate," he said.
Syrian forces, bolstered by Russian air power, began bombing the country's north-west region, including the mainly rebel-held province of Idlib, at the end of April.
A senior UN official told the Security Council on Thursday that an estimated 400,000 people have fled their homes in Syria's north-west in the last four months.
Moscow's veto was not a surprise. It has vetoed around 13 draft Security Council resolutions on Syria over the eight years of war to protect its ally, Syrian President Bashar al-Assad.
The rival draft resolution, tabled by Moscow and Beijing on Wednesday without prior discussions with other council members, was also voted down.