French PM Manuel Valls and US Secretary of State John Kerry said civilians were dying in Russian air strikes.
Russian PM Dmitry Medvedev said there was "no evidence of our bombing civilians, even though everyone is accusing us of this".
One observers' group says at least 1,015 civilians have been killed in Russian air strikes.
The UK-based Syrian Observatory for Human Rights said late last month that close to a quarter of those killed were under the age of 18.
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Russia, an ally of Syrian President Bashar al-Assad, has consistently denied hitting civilian targets and insists it is battling terrorists.
Mr Valls said his government "respects Russia and Russia's interests" but "that to re-discover the path to peace, to discussion, the Russian bombing of civilians has to stop".
Mr Kerry again accused Russia of using so-called 'dumb bombs' in Syria that do not hit precise targets. Last week, he said women and children were being killed "in large numbers" by Russian raids.
Mr Medvedev said Russia was "not trying to achieve some secret goals in Syria", adding that "we are trying to protect our national interests".
Their comments were made at a security conference in Munich, days after world powers agreed a deal to push for a cessation of hostilities in Syria within a week.
Agreement to try to bring about a cessation of hostilities and allow more access for humanitarian aid was reached by world powers late on Thursday in Germany, but neither the Syrian government nor the rebels were involved.
Under the plan, efforts will be made to try to make urgent aid deliveries to besieged and hard-to-reach areas in Syria. Steps will also be taken to work towards an eventual ceasefire and implementation of a UN-backed plan for political transition in Syria.
The halt will not apply to the battle against jihadist groups Islamic State (IS) and al-Nusra Front.
The tentative deal reached here in Munich to pause the fighting in Syria was always going to be a tough sell to the warring parties on the ground. Now its chances of success look even slimmer - "Forty-nine per cent," said Russia's foreign minister. "Closer to zero," said his British counterpart.
For much of the day the Russian and Western ministers have been trading accusations and counter-accusations as to who is to blame for the ongoing misery that is the Syrian civil war.
France, Britain and the US all accused Russia of targeting mainstream rebels and civilians with air strikes while leaving so-called Islamic State largely unscathed. Russia flatly denied this, saying most of those civilians were being besieged by rebels rather than by Assad's forces. Again, Western delegates disagreed.
So there are clearly two, diametrically opposed, versions of what is going on in Syria. That leaves little prospect of the concerted effort for peace by all parties that is so desperately needed.
Rebel groups in Syria have told the BBC they would not stop fighting because they do not believe that Russia will end its bombing campaign in support of the government.
They also reiterated their demand that President Assad be removed from power. On Friday, the president said he wanted to retake "the whole country" from rebels.
But US state department spokesman Mark Toner said Mr Assad was "deluded" if he thought there was a military solution to the conflict.
Syrian government forces, backed by Russian air strikes, have almost encircled rebels in parts of the northern city of Aleppo.
More than 250,000 people have been killed and some 11 million displaced in almost five years of fighting in Syria.
In another sign of the complexity of the conflict, reports said that on Saturday Turkish forces had shelled Kurdish militia targets in Aleppo provinces.
The Kurdish fighters had seized territory from Islamists in recent days. Turkey views the Kurdish militia as allied to the PKK group, which has a waged a campaign against Turkish security forces for decades.
On Saturday, Turkey's Foreign Minister Mevlut Cavusoglu said Saudi Arabia would send war planes to the Turkish air base of Incirlik, from where they would attack militants in Syria from the so-called Islamic State.
Saudi Arabia is already part of the international coalition against IS.
Mr Cavusoglu also said it was possible that troops from his country and Saudi Arabia might participate in a ground operation against IS forces. The US has so far ruled out a ground invasion.
Moscow has warned against any new foreign ground intervention in the country, saying such a development could even lead to a world war.
Why is there a war in Syria?
Anti-government protests developed into a civil war that, five years on, has ground to a stalemate, with the Assad government, Islamic State, an array of Syrian rebels and Kurdish fighters all holding territory.
Who is fighting whom?
Government forces concentrated in Damascus and the centre and west of Syria are fighting the jihadists of Islamic State and al-Nusra Front, as well as less numerous so-called "moderate" rebel groups, who are strongest in the north and east. These groups are also battling each other.
How has the world reacted?
Iran, Russia and Lebanon's Hezbollah movement are propping up the Alawite-led Assad government, while Turkey, Saudi Arabia and Qatar back the Sunni-dominated opposition, along with the US, UK and France. Hezbollah and Iran are believed to have troops and officers on the ground, while a Western-led coalition and Russia are carrying out air strikes.
Pressure is increasing on Russia over civilian deaths in Syria, with France and the US urging greater caution.