The shipment of Russian-made missile systems to Syria would give the regime of Bashar al-Assad a more potent weapon against a Western-led military intervention, including enforcement of a no-fly zone, analysts say.
The S-300 is one of Russia's most sophisticated air-defense systems. Like the U.S.-made Patriot battery, it uses truck-mounted missiles and radar to strike such targets as aircraft and guided missiles more than 100 miles away.
Syria, which is engulfed in a bloody, two-year-old civil war, has begun payments on a 2010 contract with Russia to buy four of the batteries, with a total of 144 missiles, for $900 million, The Wall Street Journal has reported. Russia may not ship the systems until the second quarter of 2014 despite Assad's comments this week suggesting the first delivery was made, according to Russian press accounts.
"He has a lot of incentive to make it sound like it happened," Steven Pifer, a fellow at the Brookings Institution, a think tank in Washington, D.C., said in a telephone interview. "Bluster is not an unknown diplomatic tactic."
President Barack Obama has resisted calls from Sen. John McCain, R-Ariz., and others to lead a military intervention in Syria. At least 80,000 people have died in the uprising against Assad, according to a speech this month by Vuk Jeremic, president of the United Nations General Assembly.
McCain, who made a surprise visit to Syria this week to meet with rebels, has pressed the Obama administration to create a no-fly zone. Secretary of State John Kerry has expanded non-lethal aid to the Syrian opposition. The administration is also reportedly considering supplying equipment such as body armor and night-vision goggles.
Colin Powell, the former secretary of state and chairman of the Joint Chiefs of Staff, said diplomacy is preferred to military action at this stage of the conflict.
"We have to be very, very careful with some of the [rhetoric], 'Well, let's just go in and start bombing, let's just go in and put in a no-fly zone,'" he said during a May 26 interview with Bloomberg Television. "I wouldn't like a no-fly zone. If you want to take out the Syrian air force, take it out. Don't just fly around in circles waiting for it to come up. That won't be hard to do. But you have to understand, if that doesn't work, are you then committed to take the next steps?
"I have no use for President Assad. I've negotiated with him. He's a pathological liar. You can't trust anything he says," Powell added. "But at the same time, I'm not sure what replaces him. And the conflict will not be over just because he suddenly walks away. I think a new conflict will emerge and we'll have to determine what role we'll play in resolving that one."
Enforcing a no-fly zone would be more complicated if Russia arms the Syrians with the S-300 surface-to-air missiles in part because they would extend the range of its air defenses to include a swath of northern Israel, according to Brookings' Pifer.
"It would put Israeli aircraft operating in Israeli airspace at risk," he said.
Indeed, Yaakov Amidror, the Israeli national security adviser, this week warned European diplomats that Syria's S-300s will never become operational.