Syrian President Bashar al-Assad said Sunday that the success of Russia's military intervention in his country's civil war was vital for the entire region.

"The alliance among Russia, Syria, Iraq and Iran must succeed or else the whole region will be destroyed," Assad said in an interview broadcast by Iranian state television, his first public remarks since Russia began its Syrian air campaign.

Assad also criticized Western countries, accusing them of fueling terrorism by supporting rebel groups, and fueling the refugee crisis.

"In reality, they are the biggest contributor for reaching this stage by supporting terrorism and imposing a siege on Syria," Assad said. "They attack terrorism but they are terrorists in their policies either by imposing the siege or by supporting the terrorists."

Assad's opponents say any political solution to Syria's four-year war must involve Assad stepping aside, although some Western states - including Germany - have softened their stance, saying he could remain during a transitional period.

But the Syrian president struck a defiant tone in remarks rebroadcast on the presidency's official Twitter account, saying it would be up to Syrians to decide who leads the country.

"Discussion about the political system or officials in Syria is an internal Syrian affair," Assad said.

A new dimension to conflict

Russia began launching airstrikes against Assad's rebel opponents on Wednesday. The Iran-backed Lebanese militia Hezbollah has also actively fought on the side of the Syrian military in a war that's claimed a quarter of a million lives and displaced millions.

British Prime Minister David Cameron lashed out at Russia, saying it is propping up a brutal dictator in Damascus.

"They are backing the butcher Assad, which is a terrible mistake for them and for the world," Cameron told the BBC. "It's going to make the region more unstable; it will lead to further radicalization and increased terrorism. I would say to them 'change direction, join us in attacking (ISIS)."

The disastrous conflict has also strained relations in the neighborhood, with Turkey and Iran at odds as they back rival factions in the conflict. On Sunday, Turkish President Recep Tayyip Erdogan singled out Tehran for defending Assad and "waging state terrorism" in Syria.

"The countries that cooperate with the [Syrian] regime will be accountable to history," Erdogan said.

US continues its own anti-IS campaign

Meanwhile, the United States said its military and allies had carried out 16 airstrikes in Syria and Iraq on Saturday against suspected "Islamic State" fighters.

Three of the six strikes in Syria hit targets near the town of Hasaka, the US military said in a statement issued Sunday. IS fighters, weapons and buildings were hit in 10 strikes near several Iraqi cities, including Kirkuk, Falluja and Ramadi, the Pentagon said.

jar/sms (Reuters, AP, AFP)