Tens of thousands took to the streets of Moscow Saturday for rival rallies opposing and supporting Russian strongman Vladimir Putin's political domination one month ahead of presidential polls.

Police said between 87,000 and 90,000 turned up for the pro-Putin rally in the west of the capital and put the number of protesters at the anti-Putin march to a square overlooking the Kremlin at around 23,000.

Syria's army randomly bombarded the protest hub of Homs early on Saturday, killing at least 260 civilians in one of the "most horrific massacres" in the country's uprising, an opposition group said.

In a statement, the Syrian National Council also called on the world to act, and demanded that Russia change its position, condemn President Bashar Assad's regime and allow democracy.

Russia's deputy foreign minister said Friday that Moscow could not support the latest U.N. Security Council draft resolution on Syria in its current form, the Interfax news agency reported.

"Some of our concerns and the concerns of those who think the same as us have been taken into consideration but all the same this is not enough for us to be able to support it in this form," deputy minister Gennady Gatilov said.

The leader of Russia's Islamist rebels ordered a halt to attacks on civilians, saying mass opposition protests showed the public no longer supported Vladimir Putin, according to a video posted Friday.

Doku Umarov, whose Caucasus Emirate group claimed atrocities including a deadly Moscow airport bombing in 2011 and a metro attack in 2010, said from now only security objects and officials would be targeted.

A new draft of a U.N. Security Council resolution to stop the violence in Syria contains concessions to Russia in an effort to overcome Moscow's objections, diplomats said on Thursday.

"They are not made explicit in the latest draft but it is very clear what they are referring to," one Western diplomat said, alluding to the doubts that Russia vowed would lead it to veto any "unacceptable" proposal.

Russia will not stop selling arms to Syria, a top defense official said Thursday, as Moscow stands by its longtime ally despite mounting international condemnation over the Syrian regime's bloody crackdown on a 10-month-old uprising.

Russia's Deputy Defense Minister Anatoly Antonov said his country is not violating any international obligations by selling weapons to Damascus.

Russia will use its veto to block any U.N. Security Council resolution on Syria that it deems to be unacceptable, Moscow's envoy to the United Nations said on Wednesday, as Paris said Russia has now a "less negative" attitude towards a draft resolution proposed by the West and the Arab League.

"If the text is unacceptable then we will vote against," Vitaly Churkin was quoted as saying by the RIA Novosti news agency.

Russian strongman Vladimir Putin refused to rule out on Wednesday a run-off in March presidential polls where he will seek a third Kremlin term but warned a second round risked causing instability.

"I understand that a second round run-off is possible, according to the current legislation," Russian news agencies quoted Putin as saying at a meeting with Russian election observers.

Moscow will not tell Bashar al-Assad to stand down, Russian Foreign Minister Sergei Lavrov said, stressing that while the Syrian president was not an ally it was not up to other nations to interfere.

After 10 months of internal conflict in Syria that the United Nations says has killed more than 5,400 people, Russia is under growing pressure to take a firmer line on Assad and his regime.

Fearing the loss of its last Arab ally and seeking to reassert its global clout, Russia is defiantly refusing to budge in a high-stakes diplomatic standoff with the West over the crisis in Syria.

Russia, a veto-wielding U.N. Security Council member, has exasperated the West by insisting it will not back a new resolution calling on President Bashar al-Assad to step down despite the escalation of violence between the regime and the opposition.