MOSCOW: Russia's defiance of international efforts to end Syrian President Bashar Assad's crackdown on protests is rooted in a calculation that it can keep a Mideast presence by propping up its last remaining ally in the region — and has nothing to lose if it fails.

The Kremlin has put itself in conflict with the West as it shields Assad's regime from United Nations sanctions and continues to provide it with weapons even as others impose arms embargoes.

But Moscow's relations with Washington are already strained amid controversy over U.S. missile defense plans and other disputes. And Prime Minister Vladimir Putin seems eager to defy the U.S. as he campaigns to reclaim the presidency in March elections.

"It would make no sense for Russia to drop its support for Assad," said Ruslan Pukhov, head of the independent Center for Analysis of Strategies and Technologies. "He is Russia's last remaining ally in the Middle East, allowing it to preserve some influence in the region."

Moscow may also hope that Assad can hang on to power with its help and repay Moscow with more weapons contracts and other lucrative deals.

And observers note that even as it has nothing to lose from backing Assad, it has nothing to gain from switching course and supporting the opposition.

"Russia has crossed the Rubicon," said Igor Korotchenko, head of the Center for Analysis of Global Weapons Trade.

He said Russia will always be marked as the patron of the Assad regime regardless of the conflict's outcome, so there's little incentive to build bridges with the protesters.

"Russia will be seen as the dictator's ally. If Assad's regime is driven from power, it will mean an end to Russia's presence," said Fyodor Lukyanov, editor of the magazine Russia in Global Affairs.

Syria has been Moscow's top ally in the Middle East since Soviet times, when it was led by the incumbent's father, Hafez Assad. The Kremlin saw it as a bulwark for countering U.S. influence in the region and heavily armed Syria against Israel.

While Russia's relations with Israel have improved greatly since the Soviet collapse, ties with Damascus helped Russia retain its clout as a member of the Quartet of international mediators trying to negotiate peace between Israel and the Palestinians.

After Bashar Assad succeeded his father in 2000, Russia sought to boost ties by agreeing to annul 73 percent of Syria's Soviet-era debt. In the mid-2000s, Putin said Russia would re-establish its place in the Mideast via "the Syria route."

Syria's port of Tartus is now the only naval base Russia has outside the former Soviet Union. A Russian navy squadron made a call there this month in what was seen by many as a show of support for Assad.

For decades, Syria has been a major customer for the Russian arms industries, buying billions of dollars' worth of combat jets, missiles, tanks and other heavy weapons. And unlike some other nations, such as Venezuela, which obtained Russian weapons on Kremlin loans, Assad's regime paid cash.

The respected newspaper Kommersant reported this week that Syria has ordered 36 Yak-130 combat jets worth $550 million. The deal, which officials wouldn't confirm or deny, may signal preparations for even bigger purchases of combat planes.

Korotchenko said Syria needs the jets to train its pilots to fly the advanced MiG-29M or MiG-35 fighter jets it wants to purchase: "It's a precursor of future deals."

Korotchenko said Syria's importance as a leading importer of Russian weapons in the region grew after the loss of the lucrative Iraqi and Libyan markets.

Russia, whose abstention in a U.N. vote cleared the way for military intervention in Libya, later voiced frustration with what it described as a disproportional use of force by NATO.

The Kremlin has vowed not to allow a replay of the Libyan strategy in Syria, warning that it would block any U.N. resolution on Syria lacking a clear ban on any foreign military interference.

Moscow accuses the West of turning a blind eye to shipments of weapons to the Syrian opposition and warns it won't be bound by Western sanctions.

Earlier this month, a Syria-bound Russian ship allegedly carrying tons of munitions was stopped by officials in Cyprus, an EU member, who said it was violating an EU arms embargo. The ship's captain promised to head to Turkey but then made a dash to Syria.

Asked about the ship, Russia's foreign minister bluntly responded that Moscow owes neither explanation nor apology to anyone because it has broken no international rules.

Nonetheless, Moscow has shown restraint in its arms trade with Damascus, avoiding the sales of weapons that could significantly tilt the military balance in the region.

In one example, the Kremlin has turned down Damascus' requests for truck-mounted Iskander missiles that can hit ground targets 280 kilometers (175 miles) away with deadly precision. While the sale of such missiles wouldn't be banned under any international agreements, Moscow has apparently heeded strong U.S. and Israeli objections to such a deal.

Moscow also has stonewalled Damascus' request for the advanced S-300 air defense missile system, only agreeing to sell short-range ground-to-air missiles.

"Russia has taken a very careful and cautious stance on contracts with Syria," Korotchenko said.

The most powerful Russian weapon reportedly delivered to Syria is the Bastion anti-ship missile complex intended to protect its coast. The Bastion is armed with supersonic Yakhont cruise missiles that can sink any warship at a range of 300 kilometers (186 miles) and are extremely difficult to intercept, providing a strong deterrent against any attack from the sea.

Observers in Moscow said that Russia can do little else to help Assad. The chief of the Russian upper house's foreign affairs committee, Mikhail Margelov, openly acknowledged that this week, saying that Russia has "exhausted its arsenal" of means to support Syria by protecting it from the U.N. sanctions.

Lukyanov said Russia has made it clear it would block any attempts to give U.N. cover to any foreign military intervention in Syria, but wouldn't be able to prevent Syria's neighbors from mounting such action.

"Russia realizes that it has limited opportunities and can't play a decisive role," he said.

Pukhov also predicted that Russia wouldn't take any stronger moves in support for Damascus.

"Going further would mean an open confrontation with the West, and Russia doesn't need that," he said.