62 Syrian soldiers have been killed in a US-led airstrike, it has been reported. US Central Command admitted its planes unintentionally carried out the attack in eastern Syria.
US military officials said the attack in Deir al-Zour was immediately halted "when coalition officials were informed by Russian officials that it was possible the personnel and vehicles targeted were part of the Syrian military".
The US Central Command statement said the coalition believed it was attacking positions of so-called Islamic State, according to Sky News. "Combined Air Operations Center had earlier informed Russian counterparts of the upcoming strike.
"Syria is a complex situation with various military forces and militias in close proximity, but coalition forces would not intentionally strike a known Syrian military unit. The coalition will review this strike and the circumstances surrounding it to see if any lessons can be learned."
The Russian defence ministry said the strike on Syrian troops is the consequence of Washington's refusal to co-ordinate military action with Moscow. The Syrian statement added that the air strikes had allowed IS to advance in the region and served as "conclusive evidence" that the US and its allies supported the jihadist group.
Russia said it was calling an emergency meeting of the UN Security Council over the US air strikes while issuing a stern warning that the attacks have seriously jeapoardised the US-Russia peace plan for Syria.
Gen Viktor Poznikhir said that while Russia has attempted to secure the Syrian troops, the US has failed to adhere to the terms of the peace agreement. Russia's Defence Ministry said it believed the ceasefire had been breached 199 times by rebels, adding that the US would be responsible if it were to collapse.
"If the American side does not take the necessary measures to carry out its obligations... a breakdown of the ceasefire will be on the United States," he said. "The United States and the so-called moderate groups they control have not met a single obligation they assumed in the framework of the Geneva agreement."
President Vladimir Putin said Moscow was keeping to its obligations under the truce, and the Syrian government was "fully abiding" by the agreement.
A US National Security Council spokesman later said: "While there have been challenges on both sides, violence is considerably lower and the cessation is broadly holding. What we're not seeing is humanitarian aid getting through and it will be hard to build confidence on the ground until that occurs."
There have, however, been reports of an escalation in violence in the past 24 hours, resulting in 55 rebel and the deaths of 12 civilians, BBC News reports.
The current ceasefire, brokered by US Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov, came into effect at sunset on Monday (12 September). It called for a nationwide cessation of hostilities in the war-torn region, which must hold for seven days, after which according to the terms of the peace deal, the US and Russia will begin coordinated action against the al-Nusra Front, and IS.
The ceasefire has so far, held for five days, despite claims of violations on both sides.