The US military renewed contacts with Russia on Friday to discuss how their forces can keep out of one another's way in Syria, even as Moscow deployed fighter jets to the war zone.
US secretary of defence Ash Carter and Russia's defence minister Sergei Shoigu spoke by telephone, spokespersons from their ministries said.
Washington and its NATO allies broke off ties with the Russian military in April last year in protest at Moscow's intervention in Ukraine.
But now the rivals find themselves enmeshed in Syria, where they face an opportunity to work together but also the danger of an accidental clash.
For a year, the United States and a coalition of Western and Arab allies have been carrying out air strikes against Islamic State jihadists.
The United States has also, with limited success, been training Syrians who are fighting the extremist IS group but who are also in revolt against the Damascus regime.
Russia, meanwhile, is providing support to Bashar al-Assad's government and building up its own military presence at an airbase and a naval depot in western Syria.
In addition to the tanks, armored cars and trucks that have been spotted at the Latakia airbase in recent weeks, four Russian fighter jets are on the ground there, a US official told AFP.
"The secretary and the minister talked about areas where the United States and Russia's perspectives overlap and areas of divergence," Pentagon spokesman Peter Cook said.
Russian defense ministry spokesman Igor Konashenkov told Russian agencies that the call had lasted an hour and was focused on "efforts to combat international terrorism."
"The conversation showed that the two points of view are similar or the same on most of the issues discussed," he added.
According to Cook, Kerry "emphasized the importance of pursuing such consultations in parallel with diplomatic talks that would ensure a political transition in Syria.
"Both the secretary and the minister agreed to continue their dialogue."
The renewal of contacts marks a new but begrudging willingness by Washington to engage with Russia, after months of giving President Vladimir Putin the cold shoulder over his actions in Ukraine.
But a spokesman for the State Department, Mark Toner, insisted that simply trying to find ways to avoid the forces bumping into one another in the war zone does not imply a renewal of military ties.
"The high-level military-to-military contact and cooperation with Russia that we suspended in response to Russia's illegal occupation and attempted annexation of Crimea still remains in effect," he said.
"We want to see... a de-confliction mechanism put in place if Russia intends to move forward with some kind of new effort on the ground in Syria, again, at a much more operational level."
Putin has provided vital support to Assad through a popular uprising against his regime and as the conflict has metastasized into a brutal civil war that has killed 240,000 people and displaced millions.
Moscow has also sought to portray Assad's army as a shield against Islamist rebels, including IS, which has seized a vast swathe of eastern Syria and northern Iraq and declared a so-called "caliphate."
Washington and its European, Turkish and Arab allies view Assad as a pariah who they blame for plunging Syria into chaos and allowing the Islamic State group to thrive.
But, with Western efforts to tackle the Islamic State group floundering, and the moderate Syrian opposition losing ground to radicals, the US officials have suggested Russia may have a role to play in the fight.