The strike occurred Saturday in an eastern part of Syria that is not a part of a delicate and nearly week-old ceasefire. The US military said it was targeting ISIS militants and if it hit Syrian troops, it was an accident.
Russia and Syria said the strikes prove Washington and its allies are sympathetic to ISIS.
The Russian military said 62 Syrian soldiers were killed near Deir Ezzor Airport, according to state media. The UK-based Syrian Observatory for Human Rights put the death toll at 83 and said at least 120 soldiers were wounded.
Russia's permanent UN representative, Vitaly Churkin, questioned the timing of the strikes, two days before Russian-American coordination in the fight against terror groups in Syria was to begin.
"I have never seen such an extraordinary display of American heavy-handedness," he said, after abruptly leaving an UN Security Council meeting on the situation in Syria. Churkin was upset with US ambassador Samantha Power, who lambasted Russia's support of the Syrian regime to the media outside the meeting while he was speaking.
Power angrily denounced the Russian call for the UN meeting as a stunt.
Power said "even by Russia's standards, tonight's stunt -- a stunt replete with moralism and grandstanding -- is uniquely cynical and hypocritical."
If US-led coalition airstrikes did hit Syrian forces Saturday, it was unintentional and Washington regrets any loss of life, she said before proceeding to list atrocities she said the Syrian regime has perpetuated during the five-year civil war.
"Since 2011, the Assad regime has been intentionally striking civilian targets with horrifying, predictable regularity. They have besieged civilian areas, prevented life-saving aid from reaching people who are starving to death, and dying of illnesses that could be treated with basic medicine."
Whether the diplomatic squabbling will cause the ceasefire to fall apart is unclear.
Report: At least 62 killed
The US military said the coalition thought it was hitting ISIS militants, but hours later said the airstrike may have struck Syrian soldiers.
Although the US hasn't officially said Syrian troops were killed, a senior administration official told CNN late Saturday the US relayed its regret through Russia for the "unintentional loss of life."
A statement from US Central Command said the coalition conferred with the Russian military before the strike.
"The coalition airstrike was halted immediately when coalition officials were informed by Russian officials that it was possible the personnel and vehicles targeted were part of the Syrian military," US Central Command said.
A US official told CNN they broadly described the geographic area to the Russians -- as is customary -- before the strike but did not give a precise location. The coalition thought it was going after an ISIS tank position.
Russia blames the United States
Syrian troops have been battling ISIS in Deir Ezzor for years, and the Islamist militants control most of the city.
"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," CENTCOM said.
Russia blamed the United States for failing to coordinate with them on the airstrikes, a Russian Defense Ministry spokesman told Sputnik.
"If this airstrike was carried out due to an error in the coordinates of the target, it is a direct consequence of (the) US side's unwillingness to coordinate its actions against terrorist groups with Russia," Sputnik quoted the spokesman as saying.
ISIS militants launched an attack on the Syrian position after the airstrikes, Sputnik reported, citing the Russian Ministry of Defense. Syrian state-run news agency SANA said the military was able to regain control of the area ISIS held briefly.
The Syrian military said it viewed the strike as evidence the United States and the coalition support ISIS. It called the incident a serious and blatant aggression, SANA reported.
Russia's Foreign Ministry had similar words, according to spokeswoman Maria Zakharova. She said Russia had concluded the White House is defending to ISIS. She also said that the United States didn't communicate its intention to carry out operations in the area.
The latest ceasefire has offered some respite from violence in the civil war, which has killed an estimated 430,000 people since 2011 and touched off an international refugee crisis. But there have been reports of violations, and both the Russians and Americans have said the other party is not fulfilling its obligations.
The main focus of the ceasefire was to allow humanitarian aid to reach the Syrian people besieged by war. Once the humanitarian relief was in, the Russians and Americans were meant to agree on targeting jihadist factions: Jabhat Fateh Al-Sham, the former al Qaeda affiliate in Syria, and ISIS. To do that, they are supposed to set up a Joint Implementation Center.
CNN military analyst Lt. Col. Rick Francona said it is not clear now what will happen.
"This might put in danger this Joint Implementation Center that the US and the Russians are supposed to set up in the next few days to coordinate just these kinds of strikes against ISIS and to prevent just what happened," he said Saturday.