Russian air strikes in Syria have killed 403 civilians, among them 97 children, according to figures from a monitoring group.
Vladimir Putin, Russia's president, has stepped up his country's air campaign in Syria in recent weeks, targeting anti-government rebels as well Islamist fighters with Islamic State and Jabhat al-Nusra.
But the figures from the London-based Syrian Observatory for Human Rights highlight the considerable civilian toll and raises questions about the effectiveness of the strikes.
Russia began its air campaign in Syria on 30 September.
The campaign has intensified following the downing of a Russian passenger jet in Egypt's Sinai peninsula, thought to have been carried out by Islamic State.
All 224 people on board the flight were killed.
Barack Obama, the US president, said Russia needed to make a "strategic adjustment" in Syria and drop its support for Bashar al-Assad, the Syrian president.
"He [Putin] needs to go after the people who killed Russia's citizens," Obama said, referring to the downed passenger plane.
The US president was speaking in Malaysia, at the tail-end of a nine-day trip to Turkey and Asia.
Syria's conflict has dragged on for five years and the resulting chaos has allowed Islamic State to establish itself in areas spanning Syria and Iraq.
Following the Islamic State attacks in Paris that left 130 people dead there is some prospect for greater international cooperation on Syria in order to tackle the group.
Mr Obama is due to meet French President Francois Hollande on Tuesday to discuss ways to bolster the international coalition fighting Islamic State.
Mr Hollande will then head to Russia for talks with Mr Putin.
