Western countries presented the UN Security Council late Wednesday with a draft resolution on humanitarian aid for Syria but Russia so far does not back it, raising the risk of a veto.
The vote on the draft, which involved intense negotiations with Russia, Syria's main ally, is expected Friday.
Its presentation to the council was confirmed in a tweet by the Australian ambassador Gary Quinlan.
The text was sponsored by Australia, Luxembourg and Jordan and its supporters include Britain, the United States and France.
The text, a copy of which was obtained by AFP, calls on all parties to end sieges of densely populated areas immediately.
It lists several including the city of Homs, the Palestinian camp at Yarmuk near Damascus and Ghouta on the outskirts of the capital.
It also calls for an immediate end to all attacks on civilians including aerial bombardments, especially with so-called barrel bombs -- in reference to a tactic used by the Syrian army in the northern city of Aleppo.
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The text also calls on all parties, in particular the Syrian authorities, to authorize UN agencies and NGOs access to swift, safe and unfettered humanitarian aide, including across frontlines and borders.
This cross-border access has been sought for some time by humanitaran groups so aid can be shipped directly into Syria from neighboring countries such as Iraq or Turkey. The government has refused so far.
The demands are addressed to both sides in the war but especially the government, as the text said it is mainly responsible for protecting civilians.
The resolution has no clause allowing for sanctions in case of non-compliance.
But it leaves this option open for the council if Secretary General Ban Ki-moon deems it appropriate. Ban would have 30 days once the text is passed to decide if additional measures are needed in case of non-compliance.
But this would require another vote by the council and Russia is likely to veto it.
Diplomats say Moscow is adamantly against any explicit mention of sanctions against Syria, and throughout the discussions within the council tried to soften criticism of the government of President Bashar al-Assad.
Since the Syrian crisis started in March 2011, Russia has vetoed three resolutions aimed at increasing pressure on the Syrian regime. Each time, China supported the Russian veto.