Russia has warned the West against unilateral action on Syria.
It comes a day after US President Barack Obama threatened "enormous consequences" if his Syrian counterpart used chemical or biological arms or even moved them in a menacing way.
Russian Foreign Minister Sergei Lavrov said his government and China were committed to "the need to strictly adhere to the norms of international law ... and not to allow their violation".
The remarks were a reminder of the divisions hampering efforts to end the 17-month conflict.
Russia and China have opposed military intervention in Syria and have vetoed three UN Security Council resolutions backed by Western and Arab states that would have raised pressure on Syria to end violence.
Mr Obama yesterday warned Syria that the US would not tolerate any deployment of chemical weapons, as fighting continues across the country.
He put Syrian President Bashar al-Assad's Syrian regime on notice that the US is "monitoring the situation very carefully," and has put together a range of contingency plans.
He told reporters: "There would be enormous consequences if we start seeing movement on the chemical weapons front or the use of chemical weapons ... That would change my calculations significantly."
Mr Obama added that the US would regard any recourse by Syria to its deadly arsenal as crossing what he dubbed a "red line".
Syria's admission in July that it has chemical weapons and could use them in case of any "external aggression" added a dangerous new dimension to the conflict.
In one of the latest battle zones, troops and tanks overran the Damascus suburb of Mouadamiya today, the second day of an offensive to regain control of the area.
Activists said Mr Assad's forces had killed at least 70 people in Mouadamiya since yesterday.
They included some two dozen men who had been executed and 16 people killed in a helicopter gunship attack on a funeral for victims of yesterday's violence.
"The mourners set off with 19 bodies and came back with 35," one of the activists said from the suburb.
The Syrian conflict is also affecting neighbouring states.
At least five people were killed in Lebanon in sectarian violence linked to the Syria conflict, while Turkey investigated possible Syrian involvement in a car bomb that killed nine people yesterday.
More than 130 people were reported killed in shelling yesterday in Daraa as the United Nations brought an end to its troubled observer mission.
