Russia has called a US decision to ease restrictions on arming Syrian opposition groups a "hostile act" that would directly threaten Russian military forces in Syria.
Maria Zakharova, Russian foreign ministry spokeswoman, said on Tuesday the policy change set out in the annual defence policy bill signed into law by US President Barack Obama last week, would lead to weapons ending up "in the hands of jihadists with whom the sham 'moderate' opposition have long acted jointly".
The bill gives the next US administration under Donald Trump the authority to send Syrian rebels surface-to-air missiles.
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"Such a decision is a direct threat to the Russian air force, to other Russian military personnel, and to our embassy in Syria, which has come under fire more than once. We therefore view the step as a hostile one," Zakharova said in a statement.
Reporting from Moscow, Al Jazeera's Natasha Ghoneim said Russia is "lashing out" at the United States in the final days of Obama's administration.
"The [Russian] foreign ministry is saying that the Obama administration is trying to complicate the global situation ahead of the President-elect Donald Trump taking office," she said.
Campaign of air strikes
Throughout the Syrian civil war, the US has funded several Syrian rebel groups and provided them with logistical support as well as weapons.
Russia, on the other hand, launched a campaign of air strikes last year in support of President Bashar al-Assad and his government forces to battle the Syrian opposition groups, some of which are supported by the US.
Last week, the Syrian government recaptured previously rebel-held eastern Aleppo after an intense battle that led to the displacement of tens of thousands of civilians. Many other civilians were caught in the crossfire.
Zakharova accused the Obama administration of trying to "put a mine" under the incoming administration of Donald Trump by attempting to get it to continue what she called the "anti-Russian line" of the US.
|Many of those wounded in Aleppo have been evacuated to neighbouring Turkey [EPA/SANA]
The Russian Interfax news agency cited Sergey Lavrov, Russia's foreign minister, on Tuesday as saying that the Syrian government was taking part in talks - coordinated by Russia - with the opposition.
However, the reports have been rejected by some members of the Syrian opposition.
Al Jazeera's Hashem Ahelbarra, reporting from Gaziantep in Turkey near the border with Syria, said there is a clear attempt by the Russians, the Turks and the Iranians to find a political solution to the war, with talks possibly to be held in Kazakhstan.
The Syrian National Council , the political umbrella of the Syrian opposition groups, "has distanced itself from the talks, saying that they so far have not met the Russians", he said.
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"At the same time, there are many powerful armed groups which are involved in those talks," which shows there "is a widening rift between the different Syrian factions".
Meanwhile, the Syrian government along with its ally Hezbollah, the Lebanese armed group, has stepped up its efforts to take control of rebel-held Wadi Barada on the outskirts of the capital Damascus.
Dozens of civilians were reportedly killed in barrel-bomb attacks on the area on Monday.
The Wadi Barada valley, a mountainous area near the Lebanese border, has been under siege since 2014 with food, water and electricity all in short supply.
The area is crucial for the government as it contains a vital river supplying drinking water to Damascus.
| Syrian forces took back previously rebel-held eastern Aleppo recently [Khalil Ashawi/Reuters]
The operation was launched after the Syrian government accused the rebels of contaminating the water with diesel.
The Syrian civil war started as a largely unarmed uprising against Assad in March 2011, but quickly developed into a full-on civil war.
Staffan de Mistura, the UN special envoy to Syria, estimated in April that more than 400,000 Syrians had been killed since 2011.
Calculating a precise death toll is difficult, partially owing to the forced disappearances of tens of thousands of Syrians whose fates remain unknown.
Almost 11 million Syrians - half the country's prewar population - have been displaced from their homes.
Source: Al Jazeera and news agencies