Russia withdrew from its memorandum on air safety with the United States on Thursday, soon after the US conducted missile strikes on a Syrian airbase. Moscow also called the US strikes on Syrian President Bashar al-Assad's government "aggression against a sovereign state."
Russia is a Syrian ally and backs Assad in the country's six-year long civil war, while the US has long advocated for the Syrian dictator's ouster. Despite their differing stand on Assad, Washington and Moscow have joined hands in fighting the Islamic State (ISIS) militants in the region.
The US strikes on the Syrian airbase came after a horrific chemical attack on the residential part of Syria's Khan Sheikhun killed 70 civilians, including 20 children and 13 women. Syrian activists claimed that the attack had come from the Assad-led government's airstrikes and the Syrian army denied involvement in the chemical airstrike.
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The Russian Ministry of Foreign Affairs, late on Thursday, ended the US-Russia agreement seeking to minimise the risk of any inflight incidents in Syria.
The memorandum of understanding between the nations was reached in 2015, when Russia began its official military campaign to support Assad. The deal between Washington and Moscow included general safety protocols for aircrews to follow, like maintaining professional airmanship, and also specific provisions to avoid collision and unwanted conflict, like use of specific communication frequencies and the establishment of a communication line on the ground.
Ministry of Foreign Affairs spokeswoman Maria Zakharova called the US airstrikes on Syria "thoughtless" and questioned Washington's commitment of fighting terrorism.
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Zakharova said that while previous airstrikes conducted by the US were "explained with the objective of combating terrorism, now we see an open act of aggression against sovereign Syria."
Zakharova also called for an emergency meeting of the United Nations Security Council, while Kremlin spokesperson Demitry Peskov said that the US airstrikes will seriously damage relations between the US and Russia.
"This step by Washington deals a significant blow to Russian-U.S. relations, which are in a sorry state as it is," Peskov told state news agency Itar-Tass. Peskov added that the Russian President considers the US strike on Russia a "violation of the norms of international law."