Moscow: Russia, the main military backer of the Syrian government, vowed on Friday to strengthen Syria's air defenses following a US missile strike on Syrian state forces, DPA reported.
The US conducted the strike on an airbase that it said was responsible for a chemical weapons attack that killed dozens of civilians earlier this week.
Russia has previously said it was sending powerful S-300 anti-aircraft missile systems to Syria, particularly to protect key infrastructure.
Russian President Vladimir Putin on Friday condemned the US missile strike as a violation of international law.
Putin described the attack as "aggression against a sovereign country," according to comments his spokesman relayed to state media.
The missile strike is considered the first deliberate US attack on Syrian state forces under US President Donald Trump, who has previously said he would try to enhance cooperation with Russia in Syria.
Russia has rejected the US allegations that the Syrian military was responsible for the chemical weapons attack, instead blaming militants, according to a Russian Foreign Ministry statement.
The Syrian military said that at least six people were killed and heavy damage was inflicted in the US strike, which targeted the Shayrat airbase in central Syria.
More than 50 Tomahawk missiles were launched from two US warships in the eastern Mediterranean Sea, the Pentagon said.
In response, Russia has also decided to suspend an agreement with the US on military cooperation in Syria. The deal was designed to prevent possible military incidents between the two great powers, which support opposing sides in Syria's bloody civil war.
Russia's Foreign Ministry, which announced the deal's suspension, said the US actions were further damaging the already frayed relations between the two great powers.
The tension comes just days before US Secretary of State Rex Tillerson is scheduled to visit Moscow for talks with his Russian counterpart Sergei Lavrov.
Lavrov has denounced the US missile strike as military aggression against a sovereign state, reminiscent of the US invasion of Iraq in 2003, according to comments carried by state media.
More than 80 people were killed earlier this week in the chemical weapons incident in the rebel town of Khan Sheikhoun, in the province of Idlib. "There can be no dispute that Syria used banned chemical weapons," Trump said, explaining the decision to conduct the missile strike.
Syria "violated its obligations under the chemical weapons convention and ignored the urging of the United Nations Security Council," Trump said.