(CNN) US intelligence and military targeting experts have drawn up a preliminary list of Syrian chemical weapons facilities that could be struck if President Donald Trump were to order a new round of airstrikes in the country, multiple US officials tell CNN.

A decision to take action has not been made, but one administration official with direct knowledge of the current situation told CNN the military "could respond very quickly" if Syria launched a chemical weapons attack, and the initial targeting data assembled would give the Pentagon a head start if the President decides to take action.

US officials stress they are worried that an impending Assad regime assault on the rebel stronghold of Idlib could involve the use of chemical weapons if the rebels are able to slow regime advances. The regime has moved armed helicopters closer to Idlib in the last few weeks, according to two defense officials. The US is concerned they could eventually be used to launch another chemical attack using chlorine-filled barrel bombs, though they are readily available for a conventional assault.

Officials stress they are also worried that an assault on the city using conventional weapons could leave thousands dead and deepen the humanitarian crisis along the Syria-Turkey border.

Diplomatic tensions rising

Diplomatic tensions with Russia are also rising over Idlib. On Friday, US Secretary of State Mike Pompeo warned Russia's foreign minister on Twitter: "Sergey Lavrov is defending Syrian and Russian assault on Idlib. The Russians and Assad agreed not to permit this. The U.S sees this as an escalation of an already dangerous conflict."

Sergey Lavrov is defending Syrian and Russian assault on #Idlib. The Russians and Assad agreed not to permit this. The U.S sees this as an escalation of an already dangerous conflict. — Secretary Pompeo (@SecPompeo) August 31, 2018

On Thursday, Lavrov told Western nations not to "play with fire" over Idlib.

"It's well known that the progress of Syrian resolution, humanitarian solutions and fight against terrorism is not to everyone's liking," Lavrov said, adding that the White Helmets, a group of unarmed volunteer rescue workers, were preparing to stage a chemical strike to blame on the Syrian government as a pretext for military action.

"Another such provocation is being prepared in order to hinder the anti-terroristic operation in Idlib, and we, having our facts on the table, through our Defense Ministry and Foreign Ministry clearly and firmly warned our Western partners -- don't play with fire," Lavrov said.

On Friday, the Pentagon responded, "Russia has recently launched a concentrated disinformation campaign to discredit the United States and international partners and allies... Specifically, Russia has suggested that as a pretext for United States strikes against the Assad regime, humanitarian organizations in Syria were planning a chemical weapon attack. This is absurd," Pentagon spokesperson, Cmdr. Sean Robertson said.

"That Russia is seeking to plant false lies about chemical weapons use suggests that Moscow is seeking to deflect from its own culpability when these heinous weapons are used. Russia's efforts to obscure the truth only underscore its years-long role in abetting the murder and mayhem conducted by the Assad regime," Robertson added.

Pentagon monitoring Russian activity in Mediterranean

The Pentagon is also closely watching Russian military maneuvers in the eastern Mediterranean. The Russian Ministry of Defense says 26 warships and more than 30 combat aircraft will be part of what the Russians say will be large scale exercises the area.

A US official with direct knowledge of the latest assessments tells CNN the US believes the Russians may have engaged in the buildup of naval warships to be ready for what they believe might be US strikes in response to the Assad regime using chemical weapons.

By having so many ships there, the Russians can attempt to use their shipborne radars to blanket that area and "see" any potential US Tomahawk missiles coming, the official says. One scenario the US is considering is that Russian shipborne radars could then cue Russian S-400 class anti-air systems on the ground in Syria and try to shoot US missiles down.

This would give the Russians a better chance of shooting down US missiles than in April 2018 when Russia was unsuccessful after the US, UK and France launched strikes against targets at three sites after an alleged chemical weapons attack on civilians in the Damascus enclave of Douma.

The US intelligence community has a very good understanding of what the Russians are trying to do with this seaborne strategy, officials tell CNN. It is also well known that the US military could use jamming and electronic warfare countermeasures against any Russian military efforts. In the April strikes against Syrian chemical targets, US and allied ships and aircraft fired from not only the Mediterranean but the Red Sea and North Arabian Gulf to avoid Russian detection.

The State Department has shared concerns about "any kind of escalation" of violence in Idlib with the Russian government, according to State Department spokesperson Heather Nauert. "We have shared the concerns that we have about any potential offensive taking place, we have shared those concerns with the Russian government at many levels," she said Wednesday.

As US intelligence continues to look at Russian military strategy and motivations, the official also points out the Russian naval presence contradicts all of Moscow's public statements about the situation. The US views this move by the Russian as evidence they are indeed aware the regime would be the one responsible if chemical weapons are used the official says.

The US has said they will hold the Assad regime accountable if chemical weapons are used in an attempt to retake Idlib, according to an NSC official. National security adviser John Bolton also issued a public warning, saying in Israel last week: "Just so that there is no confusion here, if the Syrian regime uses chemical weapons, we will respond very strongly. And they really ought to think about this a long time before they come to any decision because there is no ambiguity in the US position on this point."