Russian warplanes have conducted more air raids in Syria, which it says are targeting strongholds of IS. But several countries allege that Moscow's actions are also killing civilians and moderate rebels.
Russia's air campaign in Syria entered a fourth day on Saturday, with warplanes launching a number of attacks on positions of "Islamic State," including the IS stronghold of Raqqa, according to Russian news agencies and a Britain-based group monitoring Syria's civil war.
Russian news agencies cited a Defense Ministry official as saying that Russia's air force had made more than 20 flights in Syria in the past 24 hours, hitting nine IS targets.
The Syrian Observatory for Human Rights said Russian jets had targeted Raqqa, which has served as IS's de facto capital in Syria since 2013.
"Several Russian strikes hit IS positions west of Raqqa overnight and explosions were heard in the city," said Observatory head Rami Abdel Rahman.
The Observatory provides reports on Syria's conflict based on information collected from a network of activists on the ground in the country,
The Syrian Defense Ministry confirmed the strikes, saying SU-34 and SU-24M jets had destroyed an IS command post near Raqqa, as well as an underground bunker used for storing explosives.
The fresh raids come amid criticism of Russia's military operation from a number of countries that maintain that Moscow is turning a blind eye to the killing of dozens of civilians and also targeting moderate rebels opposed to Syrian President Bashar al-Assad.
On Saturday, Turkish President Recep Tayyip Erdogan said he would question Russian President Vladimir Putin as to the purpose of his military intervention in Syria.
"I will definitely speak to Putin ... I will express my sadness over this matter," Erdogan said in a transcript of an interview published by the official Anatolia agency.
"It's us who suffer in the face of the region's problems. Russia doesn't have a border with Syria. I'm troubled by what is happening now," he added.
Turkey, which has a 911-kilometer (566-mile) border with Syria, has so far taken in 2 million people fleeing the conflict.
'Recipe for disaster'
British Defense Secretary Michael Fallon said on Saturday that the overwhelming majority of the Russian airstrikes did not target IS at all.
"Our evidence indicates they are dropping unguided munitions in civilian areas, killing civilians, and they are dropping them against the Free Syrian forces fighting Assad," he said, adding that the Russian strikes were "shoring up Assad and perpetuating the suffering."
Britain itself has launched airstrikes on IS in neighboring Iraq as part of a US-led coalition, but parliament has not yet approved similar action in Syria.
US President Barack Obama warned on Friday that Moscow's military campaign in support of Assad was a "recipe for disaster."
The US favors a resolution to Syria's four-year conflict that would not include Assad, while Russia, a longtime ally of Syria, wants to see Assad continue to play a political role in the country's future.
tj/rc (AFP, Reuters)