Russian Foreign Minister Sergei Lavrov urged all "responsible countries" to act to ensure a Syrian peace conference achieves positive results, in remarks made in Iran on Wednesday.
Iran and Russia back President Bashar al-Assad's regime in the Syrian conflict, which is estimated to have killed almost 126,000 people over nearly three years.
Lavrov held talks with both Iran's Foreign Minister Mohammad Javad Zarif and President Hassan Rouhani which focused on the landmark nuclear deal between the major powers and Iran as well as the Syria peace conference dubbed Geneva 2 set for January 22.
"All responsible countries must do something so that Geneva 2 achieves a positive result," Lavrov said at a joint news conference with his Iranian counterpart.
"Those who are against (such a result) show a lack of commitment faced with the demands of the international community."
Lavrov repeatedly called Iran a "key player" that could help resolve the Syrian conflict and should be invited to Geneva.
The Syrian opposition is strongly opposed to Tehran taking part in the talks, while Assad's regime opposes any participation by leading rebel champion Saudi Arabia.
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Zarif repeated that Iran was ready to go to Geneva but "without precondition".
The Russian foreign minister said it was vital that the major powers use momentum generated by the interim nuclear deal they struck with Iran in Geneva last month to push for a full accord.
"We must start consultations for a comprehensive agreement and resolve the whole issue once and for all," Lavrov said.
Under the interim deal, which lasts for six months, Iran agreed to freeze or curb some of its controversial nuclear activities while talks continue in return for limited relief from crippling Western sanctions.
Zarif said Iran and Russia were cooperating closely on formulating the final agreement which would be the "difficult phase" the talks with the major powers, which also include Britain, China, France, Germany and the United States.
Lavrov also discussed the nuclear deal with Rouhani.
The Iranian president insisted that the interim deal struck in Geneva "recognises Iran's right to enrich uranium and those countries which interpret it otherwise are harming our common efforts to build confidence".
Rouhani was referring to the United States, which has said repeatedly that the provisions of the interim agreement expire in six months and do not represent an acceptable basis for a comprehensive deal.
President Barack Obama reiterated that interpretation on Saturday but said he did not rule out a very "modest" option for Iran to continue enriching uranium under intense outside supervision to ensure it was kept from the "breakout" capacity needed to race to build an atomic weapon.