Moscow's intervention in the Syrian conflict will have the unintended consequences of drawing Russia into a quagmire and alienating Sunni Muslims across the region, U.S. Deputy Secretary of State Antony Blinken said on Saturday.
The United States has waged an air campaign against the Islamic State militant group while also backing some non-jihadist rebel groups against Syrian President Bashar al-Assad. Russia's own air strikes aim to keep Assad in power.
"The quagmire will spread and deepen, drawing Russia further in. Russia will be seen as being in league with Assad, Hezbollah, Iran, alienating millions of Sunnis in Syria, the region and indeed in Russia itself," Blinken said at an security conference in Manama.
Syria's civil war has aggravated sectarian tensions in the region, with Iran, Lebanon's Hezbollah militia and some Iraqi militias, all Shi'ite, backing Assad against rebel groups that are overwhelmingly Sunni.
However, while Russia's involvement may increase Moscow's leverage over Assad, the conflict will also create "a compelling incentive for Russia to work for, not against, a political transition", Blinken said.
"Russia cannot afford to sustain its military onslaught against everybody opposed to Assad's brutal rule. The costs will mount every day in economic, political and security interests," he added.
Meanwhile, the United States remained "laser focused" on what Blinken called objectionable Iranian actions, including support of terrorism, in the region in the wake of its nuclear deal with major powers.
Addressing the Manama Dialogue regional security conference in Bahrain, he said U.S. engagement in the Middle East, while deeper than ever, was broad and went beyond the military aspect, adding that there was no military solution to Syria's war.
Washington has sought to reassure Gulf allies that its reluctance to actively participate in military efforts to push Assad from power does not mean it is turning its back on the region or on its traditional Arab partners.
The United States has supported a Riyadh-led Arab coalition fighting in Yemen to prevent the Iran-allied Houthi militia gaining control of Saudi Arabia's southern neighbour.
On Yemen, citizens in dire need there could not afford to wait longer for peace, and it was incumbent "on all concerned" to allow humanitarian aid to reach all who required it.