The two countries, allies of Iran, pledged their support at an emergency meeting of the International Atomic Energy Agency (IAEA) in Vienna on Thursday.
An unnamed Western diplomat said: “Russia and China have said they are going to vote for the resolution” on referral to the Security Council.
The diplomat said that if Russia went back on its promise “it would cause a problem in bilateral relations with the United States.”
The IAEA’s board of governors was meeting in emergency session, with no vote expected until Friday as the United States and Europe continued to lobby for wide support on the 35-nation body.
Iran has threatened to retaliate if it is brought before the Security Council by stepping up its nuclear work and blocking international inspections.
Russia and China made clear to IAEA non-aligned states at a meeting in Vienna on Wednesday that they stood strongly behind the resolution.
Mohamed ElBaradei, the IAEA chief, said Iran needed to do “confidence building” but he said there were no indications that Iran’s nuclear plans posed “an imminent threat”.
“We are reaching a critical phase; but it is not a crisis situation,” ElBaradei said.
The United States has sought for two years to win support for taking Iran to the Security Council, which, unlike the IAEA, has enforcement powers and can impose sanctions.
The IAEA has been investigating Iran for three years.
In September it found Iran in non-compliance with the Non-Proliferation Treaty (NPT) for hiding sensitive nuclear activities for 18 years.
Such a finding requires a report to the Security Council, but the IAEA held off on this to give Iran time to cooperate with a three-year-old agency investigation and stop nuclear fuel work.
A diplomat close to the IAEA said that referral could provoke Iran to push ahead with a programme it insists is peaceful and reduce cooperation with the agency.