Senior U.S. military officials said Friday the Pentagon is looking into whether Russia played a role in the chemical weapon attack in Syria that prompted retaliatory action from the Trump administration.

The U.S. officials said they were reviewing evidence regarding the attack on the northern Syrian town of Khan Sheikhoun, where more than 80 people were killed.

They said a drone belonging either to Russia or Syria was seen hovering over the site of the chemical weapons attack Tuesday after it happened.

The drone returned late in the day as citizens were going to a nearby hospital for treatment. The hospital was bombed shortly afterward, officials said, possibly in an effort to cover up evidence of chemical weapons usage.

The U.S. says a sarin-like nerve agent was used. Syria denies the claim. And the Kremlin says Syria's government wasn't responsible.

The U.S. officials also said they're aware of Russians with chemical weapons expertise who've been in Syria.

The United States and Russia, meanwhile, will maintain a hotline aimed at preventing midair collisions of their warplanes in Syria, senior U.S. military officials said Friday, contradicting Moscow's claims that it has suspended the "de-confliction" talks in protest of America's cruise missile strikes on a Syrian air base.

Officials blamed Russia for failing to control the Syrian government's use of chemical weapons or to account for chemical agents that were supposed to have been eliminated under a 2013 agreement, and questioned whether Russia may have been complicit in Tuesday's horrifying strike that involved the use of a sarin-like nerve gas.

In Moscow, the Russian government on Friday initially announced it would cut the hotline that was established after Russia joined Syria's civil war in 2015 to help Syrian President Bashar Assad's government against opposition groups.

The hotline's primary intent is to ensure Russian planes conducting combat missions in Syria's skies don't stumble into an accident or confrontation with aircraft flown by the U.S.-led coalition fighting an Islamic State insurgency in the north of the country.

Foreign Ministry spokeswoman Maria Zakharova reportedly said later Friday that Moscow would consider reactivating the memorandum with the United States on preventing air incidents in Syria.

"Today, everyone heard the statement of the Defense Ministry, which gave a clear assessment of this step and what motivated it," she was quoted as saying on Russian television station NTV. "We will proceed from the real situation."

But the senior U.S. military officials, who weren't authorized to speak publicly on the matter and demanded anonymity, said U.S.-Russian discussions have continued since Thursday night's attack on the Syrian military base. They said American officials asked to make sure the military talks would continue, and the Russians said they would.

Pressed on whether the Russians were actively participating in the safety calls, one official said conversations were ongoing.

Neither side had previously expressed an interest in severing the line of communication. Even when the U.S., under President Barack Obama, briefly halted talks with Russia on a Syrian peace process, both sides maintained the military communications. Eliminating the hotline could enhance the risk of an accident involving the two nuclear powers.

Fox News' Lucas Tomlinson and The Associated Press contributed to this report.