In its third display of support for Syria's embattled regime in recent weeks, Russia has reportedly signed a $550 million deal to provide Syria with 36 Yak-130 advanced training jets that can also be used for ground-attack missions.

There are persistent reports that Russia, Syria's main arms supplier and the principal diplomatic ally of President Bashar al-Assad's regime, has been supplying light arms to Syrian security forces who have been battling an uprising to topple one of the harshest dictatorships in the Middle East for 10 months.

The deal for the combat trainers, signed in December, was reported Monday by the Russian business daily Kommersant, quoting sources close to the state arms exporter, Rosoboronexport.

Damascus has been seeking the Yaks, NATO codename Mitten, primarily for use against Israel since 2008, when a high-powered Syrian procurement team visited Moscow with a $5 billion shopping list. It was understood then Syria wanted 75 of the jets.

It's not clear when the twin-engine Yak-130s, built by Yakovlev at its aviation plant in Nizhny Novgorod, southeast of Moscow, and marketed by Rosoboronexport, will be delivered.

At first glance, their arrival anytime soon is unlikely to affect the conflict raging across Syria in the near term. But if the uprising deteriorates into a full-blown civil war, as many Middle East observers feel it will if it continues much longer, the Syrian air force's capabilities against insurgent forces would be greatly enhanced.

It's not clear how the minority regime in Damascus, dominated by Assad's Alawite Muslim sect, will be able to pay for the aircraft.

Syria's economy has nosedived since the uprising erupted March 15, part of the Arab Spring upheaval across the Middle East that so far have toppled the longtime leaders of Tunisia, Egypt, Libya and Yemen.

Oil Minister Sufian Allaw disclosed Friday the state has lost $2 billion in oil revenues because of U.S. and Europeans bans on Syrian crude. Western economists say that's just a fraction of Syria's economic losses.

Rosoboronexport has yet to confirm the Yak contract. But if it is verified, it marks a major act of defiance by Moscow of international efforts to pressure Assad to step down and end 41 years of rule by his family, or negotiate with the insurgents.

Damascus has been widely condemned for throwing the full weight of its military and security forces, including tanks, against the civilian protesters demanding Assad's ouster.

For months, protesters were being killed in droves by regime forces, including the widely feared mukhabarat, or secret police, and hired guns recruited from Alawite clans.

In recent weeks army defectors and others have started fighting back, moving the conflict toward civil war.

Russia, Syria's patron during the Cold War when Assad's strongman father and founder of the dynasty ruled the country, has been a strong ally of Damascus and stood by it throughout the current bloodletting despite intense Western displeasure.

Russian Foreign Minister Sergey Lavrov warned in Moscow Monday that Russia will block any attempt to secure U.N. support for international military intervention against Syria, similar to NATO's support for Libyan rebels who ousted longtime dictator Moammar Gadhafi in August.

"We don't consider it necessary to explain ourselves or justify ourselves because we're not violating any international agreements or any Security Council resolutions," Lavrov declared last week.

In December, the Russian Interfax news agency reported Moscow had delivered 72 supersonic Yakhont SS-N-26 anti-ship cruise missiles to Damascus with two coastal-defense Bastion anti-ship systems despite calls for a U.N. arms embargo on the regime.

The 2007 contract was an estimated $300 million.

The SS-N-26, which Russia calls the P-800, has a range of 190 miles and a maximum speed of 1,900 mph. It carries a warhead of 440 pounds of high explosive, enough to sink a large warship.

On Jan. 10, Russia's only operational aircraft carrier, the 43,000-ton Admiral Kuznetsov, and other warships made a high-profile visit to the Syrian port of Tartous in a show of support for Assad.

In recent years, Moscow has provided Syria with 36 truck-mounted Pantsir SIE short-range air-defense missile systems and eight MiG-29SMT interceptor fighters.

Syria also badly wants Russian Iskandar-E tactical surface-to-surface missiles, highly accurate and reported to be one of the most advanced systems of its type in the world. U.S. and Israeli opposition has stymied any deal.