The Syrian government called USA claims about the crematorium "totally untrue" and "fabrications by the imagination of this administration and its agents".
In a statement to state-run Syrian Arab News Agency, Syria's Ministry of Foreign Affairs and Expatriates said the accusation about the crematorium was "totally baseless" and a "new Hollywood story" that is "fundamentally untrue".
The US State Department revealed "declassified" satellite images showing the Sednaya prison compound north of the Syrian capital Damascus along with the crematorium that it alleges the Assad regime is using to disguise mass killings and crimes against humanity.
The State Department, which warns U.S. citizens against all travel to Syria, believes the Assad regime is responsible for killing as many as 50 detainees per day at Sednaya, Jones said.
Although the State Department cast its unusual news conference as an effort to press Assad's key backers, Russian Federation and Iran, it also underscored Trump's lack of a strategy for stopping Syria's violence. The photos, taken over several years starting in 2013, do not prove the building is a crematorium, but show construction consistent with such a facility. But he noted that Amnesty International reported that between 5,000 and 11,000 people had died at the prison between 2011 and 2015.
The allegation of mass killings came as President Donald Trump weighs options in Syria, where the USA launched cruise missiles on a government air base last month after accusing Assad's military of killing scores of civilians with a sarin-like nerve agent.More news: Oh Snap! Shares drop 25 percent after disappointing results
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An Israeli minister says Syrian President Bashar al-Assad is to blame for the sufferings of the Arab state and should be assassinated, a day after the USA leveled fresh allegations against the Damascus government.
Syrian rebels and government officials are meeting separately with the United Nations envoy as peace talks on the war-torn Mideast country got underway in Geneva.
The allegations about the crematorium are akin to accusations about the use of chemical weapons against the opposition.
He also expressed doubts about a recent Russia-brokered deal to "de-escalate" the 6-year-old Syrian civil war, which bore Russia, Iran and Turkey as guarantors.
The Observatory says two women were killed by rocket fire in a Damascus suburbs and another was died from aerial bombardment in central Homs province. Wael Abou Rayan, a media activist in the Homs countryside, said the bombing of Homs had eased since the agreement, but never completely stopped.
Associated Press Writer Jamey Keaten in Geneva contributed to this report.