The Russian Foreign Minister Sergei Lavrov has accused the US of threatening Moscow's national security.
In an interview with Russian state TV likely to worsen already poor relations with Washington, Mr Lavrov blamed the Obama administration for what he described as a sharp deterioration in US-Russia ties.
"We have witnessed a fundamental change of circumstances when it comes to the aggressive Russophobia that now lies at the heart of U.S. policy towards Russia," Mr Lavrov said. "It's not just a rhetorical Russophobia, but aggressive steps that really hurt our national interests and pose a threat to our security."
"This is a very dangerous game given that Russia, being in Syria at the invitation of the legitimate government of this country and having two bases there, has got air defence systems there to protect its assets," said Mr Lavrov.
The remarks came as tensions continued to mount between the two powers and Russia stepped up its military presence in Eastern Europe, moving nuclear capable missiles close to Poland.
"We have witnessed a fundamental change of circumstances when it comes to the aggressive Russophobia that now lies at the heart of US policy towards Russia," state news agency RIA quoted Mr Lavrov as saying.
He continued: "It's not just a rhetorical Russophobia, but aggressive steps that really hurt our national interests and pose a threat to our security."
Most recently, tensions between Russia and the US have been fuelled by the war in Syria. Russia has taken the side of Syrian President Assad and was accused of war crimes by US Secretary of state John Kerry over the bombing of civilian and humanitarian targets.
But Mr Lavrov signalled a determination to protect Russian interests in Syria and said he hoped Barack Obama would reject any proposals of carpet bombing Syrian military air fields put to him by advisors.
In pictures: Russian air strikes in Syria
In pictures: Russian air strikes in Syria
Syrian boys cry following Russian air strikes on the rebel-held Fardous neighbourhood of the northern embattled Syrian city of Aleppo
Russian defense ministry spokesman Major General Igor Konashenkov speaks to the media in Moscow, Russia. Konashenkov strongly warned the United States against striking Syrian government forces and issued a thinly-veiled threat to use Russian air defense assets to protect them
Syrians wait to receive treatment at a hospital following Russian air strikes on the rebel-held Fardous neighbourhood of the northern embattled Syrian city of Alepp
Russian Deputy Defense Minister Anatoly Antonov speaks at a briefing in the Defense Ministry in Moscow, Russia. Antonov said the Russian air strikes in Syria have killed about 35,000 militants, including about 2,700 residents of Russia
Jameel Mustafa Habboush, receives oxygen from civil defence volunteers, known as the white helmets, as they rescue him from under the rubble of a building following Russian air strikes on the rebel-held Fardous neighbourhood of the northern embattled Syrian city of Aleppo
Civil defence members rest amidst rubble in a site hit by what activists said were airstrikes carried out by the Russian air force in the town of Douma, eastern Ghouta in Damascus, Syria
A girl carrying a baby inspects damage in a site hit by what activists said were airstrikes carried out by the Russian air force in the town of Douma, eastern Ghouta in Damascus, Syria
Civilians and civil defence members look for survivors at a site damaged after Russian air strikes on the Syrian rebel-held city of Idlib, Syria
Civilians and civil defence members carry an injured woman on a stretcher at a site damaged after Russian air strikes on the Syrian rebel-held city of Idlib, Syria
Volunteers from Syria Civil Defence, also known as the White Helmets, help civilians after Russia carried out its first airstrikes in Syria
The aftermath of Russian airstrike in Talbiseh, Syria
Smoke billows from buildings in Talbiseh, in Homs province, western Syria, after airstrikes by Russian warplanes
Russian Air Forces carry out an air strike in the ISIS controlled Al-Raqqah Governorate. Russia's KAB-500s bombs completely destroy the Liwa al-Haqq command unit
Caspian Flotilla of the Russian Navy firing Kalibr cruise missiles against remote Isis targets in Syria
Â© TASS/ITAR-TASS Photo/Corbis
Russia claimed it hit eight Isis targets, including a "terrorist HQ and co-ordination centre" that was completely destroyed
A video grab taken from the footage made available on the Russian Defence Ministry's official website, purporting to show an airstrike in Syria
A release from the Russian defence ministry purportedly showing targets in Syria being hit
Russia launched air strikes in war-torn Syria, its first military engagement outside the former Soviet Union since the occupation of Afghanistan in 1979. Russian warplanes carried out strikes in three Syrian provinces along with regime aircraft as Putin seeks to steal US President Barack Obama's thunder by pushing a rival plan to defeat Isis militants in Syria
Caspian Flotilla of the Russian Navy firing Kalibr cruise missiles against remote Isis targets in Syria, a thousand kilometres away. The targets include ammunition factories, ammunition and fuel depots, command centres, and training camps
Â© TASS/ITAR-TASS Photo/Corbis
"[Bombing Syrian bases] is a very dangerous game given that Russia, being in Syria at the invitation of the legitimate government of this country and having two bases there, has got air defence systems there to protect its assets," Mr Lavrov said.
However, the foreign minister also said Moscow was ready to continue to the search for a long term solution to the Syria crisis despite its disagreements with the West.
Elsewhere, however, unease has been growing as nuclear-capable Iskander-M missiles were moved into the Russian enclave of Kaliningrad, which is sandwiched between Nato member states Poland and Lithuania.
Polish Defence Minister Antoni Macierewicz said the country considered the matter of "highest concern" and was monitoring the situation.
Estonia, another border neighbour of Russia, is also worried about the development. The chief of staff of the Estonian Defense Forces, Lieutenant General Riho Terras, told local broadcaster ERR that he sees the move as part of a larger Russian attempt to dominate the Baltic Sea.
"In the long term, Russia's wish is to bring the Baltic Sea and the passages leading to it more and more under its control, and to control it much like it does the Black Sea," Lt Gen Terras said.
However, Russian Defense Ministry spokesman Major General Igor Konashenkov played down the concerns.
"The Iskander ballistic missile system is mobile," he said in a statement on Saturday. "As part of the plan of combat training, missile troops are engaged in training on a year-round basis, covering great distances of the Russian territory in various ways: by air, by sea, and under their own power."
He also said Russia used the deployment to determine what range a U.S. spy satellite has.
"We exposed one Iskander before loading it on the Ambal (a cargo carrier) right under a U.S. reconnaissance satellite flying above in order to verify the parameters of that space apparatus. We did not have to wait too long (for results)," he said.
Kaliningrad is the most Western Russian territory and vital to the country’s strategic interests. It is home to the Russian Baltic Fleet, as well as land forces and an air force detachment.
Russia suspended a treaty with Washington on cleaning up weapons grade plutonium earlier this month in response to what it said were "unfriendly acts" by the United States.
Mr Lavrov said both countries had the right to pull out of the treaty in the event of "a fundamental change in circumstances".
"The treaty was concluded when relations were normal, civilised, when no one ... was trying to interfere in the (other's) internal affairs. That's the fundamental change of circumstances," said Mr Lavrov.