The major powers started talks Thursday on a UN Security Council resolution on Syria with Russia declaring a "red line" against sanctions.
Russia and the Western nations on the 15-member council have drafted rival resolutions on Syria.
Britain, the United States, France and Germany have demanded sanctions against President Bashar al-Assad under Chapter VII of the UN Charter. Russia is firmly against.
"Anything can be negotiated but we do not negotiate this. This is a red line," Russia's deputy UN ambassador Igor Pankin told reporters at the Security Council after the first talks among key envoys.
Russia and China have previously twice used their powers as permanent members of the Security Council to veto resolutions which hinted at sanctions.
Signup to our newsletter and follow us on Facebook and Twitter!
The ambassadors from all 15 council countries were to meet later Thursday to discuss the two texts.
The Security Council has to pass a resolution by July 20 when the 90-day mandate for the nearly 300 unarmed UN monitors in Syria runs out.
A ceasefire brokered by UN-Arab League envoy Kofi Annan has never taken hold and the monitors suspended their operations a month ago because of the growing danger.
Syrian activists say that more than 17,000 people have died in the 16-month old conflict.
Russia has proposed a resolution which would simply roll over the mandate for the UN Supervision Mission in Syria for another three months.
The Western nations want the Security Council to give Assad a 10-day deadline to halt attacks by heavy weapons or face sanctions.