Turkey and Russia took a big step towards normalising relations this week, with President Recep Tayyip Erdogan and his counterpart Vladimir Putin announcing an acceleration in trade and energy ties.
There were also proposals on cooperation against DAESH in Syria and though the details of that effort are yet to be outlined, the United States on Thursday said the development would be a 'welcome' step in the battle against the terrorists.
"We remain in close contact with our Turkish allies and our partners in the fight against DAESH," State Department spokeswoman Elizabeth Trudeau said.
Working against DAESH "is a priority for all of us," she said.
"If this is truly a step in that direction, we would welcome that."
Pressed by reporters to confirm the US reaction, Trudeau said, "We've been very clear that if Russia is interested in fighting against (DAESH)," then "we would welcome that."
Turkish-Russian relations have warmed amid frustration in Ankara that Washington and other Western capitals did not seem more supportive after the attempted military coup against the democratically elected government last month.
Erdogan traveled to Moscow on Tuesday to meet with Russian President Vladimir Putin.
On Thursday, Turkish officials representing the army, intelligence agencies and the foreign ministry were in Russia for talks on Syria, according to Turkish Foreign Minister Mevlut Cavusoglu.
US Secretary of State John Kerry met with Putin last month to discuss coordinating the two countries' air strikes against DAESH and their allies.
Also on Thursday, the United States expressed concern about mounting reports of alleged use of chemical weapons against civilians in Syria, including during an attack in Aleppo a day earlier.
Washington is "very concerned about the increasing number of allegations of chemical weapons use over the last few weeks," Trudeau said.
The United States and Russia are responsible for overseeing a UN resolution from late 2013 to dismantle the Syrian government's chemical weapons arsenal.
Confirmation that Bashar al-Assad's regime has used such weapons since then would constitute a "violation" of the resolution, Trudeau said.