The United States said Monday it would welcome a plan for Syria to hand over its chemical weapons but expressed skepticism at the Russian initiative, which is designed to head off American air strikes.

However, the U.S. Senate announced later on Monday that it will hold a procedural vote Wednesday on a measure authorizing President Barack Obama to use military force against Syria.

Syrian President Bashar Assad's foreign minister on Monday welcomed Russia's proposal that Damascus hand over control of its chemical weapons arsenal to international supervision to avoid U.S. military action.

"I carefully listened to (Russian foreign minister) Sergei Lavrov's statement about it. In connection with this, I note that Syria welcomes the Russian initiative based on the Syrian leadership's concern about the lives of our nationals and the security of our country," Walid al-Muallem said in televised comments.

The U.S. and Russia clashed at the U.N. atomic agency Monday over Moscow's request for an IAEA probe into the risks posed by U.S. airstrikes hitting a small Syrian reactor.

The head of the International Atomic Energy Agency, Yukiya Amano, said meanwhile that there was "not a big amount" of radioactive material at the research reactor in the suburbs of Damascus.

Unknown assailants on Monday shot dead a Russian diplomat in the capital of the breakaway Georgian region of Abkhazia, also seriously injuring his wife, authorities in the separatist territory said.

"First secretary at the embassy of the Russian Federation in Abkhazia, Dmitry Vishernev, was murdered in a terrible criminal attack in Sukhumi," the Russian-backed territory's foreign ministry said in a statement.

Russian opposition leader Alexei Navalny on Monday warned of protests after narrowly failing to push Moscow's pro-Kremlin mayor into a run-off in tight elections he claimed were marred by falsifications.

Mayor Sergei Sobyanin just crept over the finish line to win 51.3 percent of votes in Sunday's poll, which analysts saw as a crucial test of the protest mood in Russia over a year into President Vladimir Putin's new Kremlin term.

Russia on Monday firmly stood by its ally Syria as President Bashar Assad's foreign minister visited Moscow, warning that military strikes against the regime would lead to an "outburst" of terrorism.

Russian Foreign Minister Sergei Lavrov, after talks with his Syrian counterpart Walid al-Muallem in Moscow, painted a dark picture of the consequences of U.S.-led military action and insisted the regime was still ready for talks.

Moscow's pro-Kremlin mayor was set to win tight elections Sunday in the Russian capital, just escaping a second-round run-off after a strong challenge from protest leader Alexei Navalny, who denounced the results as falsified.

Initial results showed that Sergei Sobyanin, a leading ally of President Vladimir Putin, would narrowly win in the first round with just over half the vote after Navalny unexpectedly picked up over a quarter of the ballots.

A Russian plane landed in the Syrian port city of Latakia on Sunday, the government said, as it seeks to evacuate its citizens from the escalating conflict.

The plane would collect citizens of Russia and other ex-Soviet states "who have expressed a desire to leave the zone of conflict," Russian emergencies ministry spokeswoman Irina Rossius said in a statement.

A top critic of President Vladimir Putin on Sunday faced a Kremlin-backed incumbent in a hotly contested Moscow mayoral poll, the first time an opposition leader has been allowed to stand in a high-profile election.

In the Russian capital's first mayoral election in a decade, Muscovites had to choose from six candidates including current pro-Kremlin mayor Sergei Sobyanin and main opposition candidate Alexei Navalny.

U.S. President Barack Obama on Friday met Russian gay rights activists after the G20 summit, in a symbol of U.S. support for the community amid a furore over an "anti-gay" Russian law.

Two gay rights activists were among a group of nine Russian civil society members Obama briefly met just before taking off from Saint Petersburg after the two-day G20 summit hosted by President Vladimir Putin.