The Syrian Foreign Ministry, while strongly condemning the accusation, further said such allegations were "totally unfounded".
The United States accused Syria on Monday of executing thousands of imprisoned political opponents and burning their bodies in a crematorium to hide the evidence, testing the U.S. administration's willingness to respond to atrocities, other than chemical weapons attacks, that it blames on Syria's regime headed by authoritarian Bashar Assad's. "Credible sources have believed that numerous bodies have been disposed in mass graves", Jones told reporters at a briefing. It represents an "effort to cover up the extent of mass murders taking place in Sednaya prison".
He said the USA claim is based on information from its intelligence community and credible humanitarian groups.
The State Department distributed overhead photographs it said documented the gradual construction of the facility outside the main prison complex and its apparent use this year.
The State Department said Monday the Assad government built a crematorium at the prison to rid itself of the bodies of the 50 or more prisoners it executes each day.
Galant says a "genocide" is underway in Syria, where an estimated 400,000 people have been killed and half the population has been displaced by a six-year-old civil war.
He said the government of Syrian President Assad "has sunk to a new level of depravity". The Astana track produced a May 4 deal to create four "de-escalation" zones across some of Syria's bloodiest battlegrounds.
The latest accusations have cast a shadow over Syria talks in Geneva, where Syrian government and opposition representatives sat down separately with the United Nations envoy.
"In light of the failures of the past ceasefire agreements, we have reason to be skeptical", Mr Jones said. "The (Assad) regime must stop all attacks on civilian and opposition forces". "But then the U.S. should understand that it bears a hefty responsibility for the future of the peace process in Syria", he said.
The U.S.is accusing Bashar al-Assad's regime in Syria of killing thousands of people from 2011 to 2015 and using a crematorium to dispose of their bodies.
Last month, in retaliation for the chemical attacks done on Syrian civilians by the government, the U.S. had launched its cruise missiles that strike on the air force base located in an undisclosed region near the Syrian capital. His administration now says Assad can not bring long-term stability to Syria.
The Russian government has said they want find a solution to the Syrian crisis; however, "there is no solution without an end to these atrocities", Jones said.