WASHINGTON (CNN) - America's top military officer, Gen. Joseph Dunford, spoke with his Russian counterpart Gen. Valery Gerasimov, on Tuesday, the same day Gerasimov threatened to target US forces in Syria should they retaliate against the regime's use of chemical weapons.
The call was first revealed by the Russian Ministry of Defense.
"The conversation focused on issues of mutual concern, to include the situation in Syria. In accordance with past practice, both have agreed to keep the details of their conversation private," Col. Patrick Ryder, a spokesman for Dunford, the chairman of the Joint Chiefs of Staff, told CNN.
Ryder said the two men had last spoken on Jan. 20.
Earlier on Tuesday, Gerasimov warned the US against any retaliatory strikes over Syria's chemical weapons use, claiming that anti-regime rebels were planning to stage a regime chemical weapons attack and saying any US strike against Damascus would threaten Russian troops.
"The United States of America plan to accuse the Syrian government troops of using chemical weapons, demonstrate so-called 'evidence' of alleged numerous victims among civilians caused by actions of the Syrian government supported by the Russian leadership," Gerasimov told a meeting of Russian military officers convened to discuss the situation in Syria.
"If lives of the Russian officers are threatened, the Armed Forces of the Russian Federation will retaliate against missile and launch systems," Gerasimov added.
US Defense Secretary James Mattis warned Syria against using chemical weapons Sunday, implying it would prompt military consequences, as it did last year when President Donald Trump ordered a strike on a Syrian air base.
"I just want to reiterate it would be very unwise for them to use weaponized gas," Mattis told reporters while en route to Oman. "And I think President Trump made that very clear early in his administration," referring to the US strike on the Syrian airbase after an aerial attack against civilians involving sarin gas.
Mattis also blamed Russia for Syria's maintenance of chemical weapons stockpile, which Russia had said it would help eliminate as part of an agreement in 2013 but which the US and international observers said Syria used on civilians last year.
"Russia was the framework guarantor that (Syrian dictator Bashar al-Assad) would get rid of all of it," Mattis said.
"Again, either Russia is incompetent or in cahoots with Assad," Mattis added.
The US ambassador to the UN, Nikki Haley, said Monday that "the United States remains prepared to act if we must," referring to alleged Russian and Syrian regime violations of the UN ceasefire intended to curb violence in Syria.
"It is not the path we prefer, but it is a path we have demonstrated we will take and we are prepared to take again," she said.
Tensions over Syria come as the UK has accused Russia of "likely" being behind an attempted assassination of a former Russian intelligence official in Salisbury involving a deadly nerve agent.
While the White House initially declined to say Russia was responsible for the attack, when speaking to reporters Tuesday Trump said that "it sounds to me like it would be Russia, based on all of the evidence they have."
"It sounds to me like they believe it was Russia and I would certainly take that finding as fact," he added.