Russia has pressed its idea of an international Syria conference including Iran and again voiced opposition to the use of force to end the deadly violence.
Moscow said that denying Tehran - a key Damascus ally - a role in helping to negotiate an end to the 17-month crisis in Syria would be "thoughtless".
"We want this event to be effective," Russian Foreign Minister Sergei Lavrov told reporters.
"To say that Iran doesn't have a place because it is already to blame for everything and it's part of the problem and not part of the solution, this is thoughtless to say the least from the point of view of serious diplomacy."
The Iranian government is one of the most important of a dwindling number of friends for Syria's embattled President Bashar al-Assad, who is facing mounting calls to go.
Lavrov said Moscow would be "glad" to support Assad's departure but only if Syrians themselves agreed on it.
Susan Rice, the US ambassador to the United Nations, has called Iran a "spoiler" and said it is "part of the problem in Syria." The United States has accused Iran of arming Assad's forces.
Russia has said a conference was needed to overcome differences over the implementation of the peace plan of UN-Arab League envoy Kofi Annan, left in tatters by the continued violence.
Lavrov said permanent UN Security Council members Russia, the United States, France, Britain and China, Syria's neighbours including Lebanon and Jordan, as well as the EU and the Arab League should take part in the get-together.
Moscow wants to hold the conference "as soon as possible", Lavrov said, without being more specific.
He stressed it might be necessary to overlook ideological divisions to settle the Syria crisis and he suggested that the United States should do so over Iran.
"Americans are pragmatists. When they want, they do not pay attention to ideological problems," Lavrov said. "This is pragmatism. It's simply necessary in foreign policy."
"We are talking about saving people's lives."
The main opposition group, the Syrian National Council, voiced doubt about involving Iran in any conference on the future of Syria.
"We are not against this idea in principle but in practice I do not see how we can bring states which still support the crimes of this regime to a conference whose goal is to find a solution," the SNC's outgoing leader Burhan Ghalioun said at a meeting in Istanbul to choose his successor.
Lavrov acknowledged that Annan's plan had begun to "seriously falter" but said the Kremlin saw "no alternative".
Diplomats said Friday that Britain, France and the United States would draw up a UN Security Council resolution proposing sanctions against Syria over the worsening conflict, which culminated in a fresh massacre earlier this week.
At least 55 people were killed in Wednesday's assault on the village of Al-Kubeir, according to activists. UN officials believe that Syrian government forces and allied militia were behind the attack.
But Lavrov again reaffirmed Russia's opposition to the use of force.
"We will not sanction the use of force at the United Nations Security Council," he said.
"The way the Syrian crisis will be solved will play a huge role in the way the world will be: whether it will rely on the UN Charter or whether it will be considered a place where the rule of force reigns."
The use of force would send shockwaves across the entire Middle East, he warned.
"All this risks the creation of a very large arc of instability from the Mediterranean to the Persian Gulf," he said, warning of "an absolutely real threat of a Sunni-Shiite standoff in the region."