Russians trying to 'cover up' what happened in Syria, US officials say The statement came as the secretary of state was set to visit Russia.

 -- Russia is trying to "cover up" what happened in the Syrian chemical attack that killed dozens of people, engaging in a campaign of “disinformation” and pointing to a “clear pattern of deflecting blame,” senior administration officials said.

In the wake of the attacks, Russia attempted to shift the blame, suggesting that a terrorist warehouse containing chemical weapons was struck during a Syrian airstrike. The Syrian government denied using chemical weapons.

“This is an opportunity for Russia to choose to stop their campaign of disinformation,” a senior administration official said in a clear shot across Russia’s bow, just before Secretary of State Rex Tillerson’s meeting with his Russian counterpart.

Senior administration officials briefed reporters at the White House on Tuesday afternoon on newly declassified intelligence that they said disproves Russian claims that the Assad regime did not launch the chemical attack in northern Syria last week.

“We are very confident that terrorists or nonstate actors did not commit the attack,” a senior administration official said, noting that they do not have sarin, the nerve agent believed used in the attack.

According to the senior administration officials, the information declassified today shows that there is no evidence of an explosion but that there is evidence of leakage that occurs after chemical weapons are dropped.

“I think it’s clear that the Russians are trying to cover up what happened there,” one senior administration official said.

It is unclear, however, if Syria still has chemical weapons.

“We take very seriously the possibility that Syria may have additional agents elsewhere,” an official said, pointing out that after a 2013 agreement, Syria “gave up a huge amount” and there was a “huge effort” to remove and destroy them.

The officials reiterated that the U.S. has not yet reached a conclusion about whether Russia knew in advance about the attack but noted the history of close cooperation between the two countries’ militaries.

“Considering the fact that there were Russian forces located with Syrian forces at the Syria airfield and, in addition to many other installations, many other Syrian regime installations around the country, we do think that it is a question worth asking the Russians — about how is it possible that their forces were located with the Syrian forces that planned, prepared and carried out this chemical weapon attack at the same installation and did not have foreknowledge?” the official said.

The officials detailed the body of evidence that last Tuesday’s attack utilized sarin, based on the hundreds of accounts of victims and symptoms consistent with the nerve agent.

The officials said that victims had miosis (constriction of the pupils), frothing at the mouth and nose and twitching and that secondary responders also showed symptoms and but no wounds suggesting a conventional attack.

In a detailed account of the attack, officials said Russian-made Su-22 fighter jets flying out of Syria's Shayrat air base were in the area of Khan Sheikhoun at the time of the attack, 6:55 a.m. on April 4, then left the area right afterward.

They added that personnel “historically associated with chemical weapons programs” were spotted at the air base in March for preparations and again on the day of the attack.