The figure is equivalent to Russia's total arms sales for 2010 and would represent a massive setback to the country's efforts to maintain its Soviet-era clients in the Middle East.

The unnamed arms export official told the Inter fax news agency that Russia was carefully monitoring the situation because it had major outstanding contracts with some of the fallen regimes.

The source said Russia "was working on and already implementing arms contracts worth some $10 billion" in the affected countries.

"Nothing can be ruled out in the current situation, and in the worst-case scenario, these plans may be wrecked," the Russian source said.

Russia sells arms across the region. Its most important Middle Eastern clients include Yemen and Libya, whose regimes are currently seeing the biggest challenge to their rule, and Egypt where Hosni Mubarak has fallen from power.

Two years ago, Libya's embattled leader Moamer Kadhafi offered to host a Russian naval base in his North African country.

The official said Russia was currently negotiating a $2 billion contract with Libya, with the entire region representing Russia's most important military client base after China and India.

"Recently, besides our main strategic partners China and India, Russia has also developed close relations with Algeria, Jordan and Syria," the arms export official said.

He added that Russia was also "implementing existing contracts with Saudi Arabia, Egypt, Libya, Yemen, Morocco, Kuwait, Qatar and other Middle Eastern and north African countries."

Russia is the world's second-largest arms exporter after the United States, accounting for 23 percent of all international weapons sales made between 2005 and 2009, according to Jane's Information Group.

The country in 2007 also began military negotiations with Saudi Arabia, a close Washington ally that last year agreed to purchase an additional $60 billion in arms from the United States.

The head of Rosoboron export, the Russian arms export company, said that all of Russia's Saudi Arabian contracts -- which were estimated at $2 billion by the Moscow media -- remained in force, the RIA Novosti news agency reported.

But officials conceded that Russia was already experiencing difficulties with Algeria, which has agreed to purchase an additional shipment of S-300 surface-to-air missiles at an undisclosed cost.

"There is a contract ... but they have experienced financial difficulties," the head of Rosoboron export was quoted as saying.

"We have recently agreed a (new) deliveries schedule, and it will be fulfilled."