America's top military officer, Gen. Joseph Dunford, spoke again with his Russian counterpart Gen. Valery Gerasimov, on Wednesday, according to a statement from a spokesman for Dunford, the second such conversation in less than two weeks.
"The conversation focused on Syria and other issues of mutual concern. In accordance with past practice, both have agreed to keep the details of their conversation private," US Air Force Col. Patrick Ryder, a spokesman for Dunford, told CNN.
Calls between the two senior officers are relatively rare but there has been increased communication in recent weeks. The two men last spoke on March 13, a conversation focused on the same issues, according to Ryder.
The last call prior to that was on January 20.
Gerasimov also spoke on the phone Wednesday with NATO Supreme Allied Commander-Europe US Army Gen. Curtis Scaparrotti, according to a statement from the Russian Ministry of Defense.
The two generals "exchanged their views on topical issues of international security," the statement said, adding that Gerasimov endorsed Scaparrotti's proposal for the two men to meet.
A NATO military official told CNN that the conversation demonstrated "a clear mutual interest to maintain the military lines of communication, in line with NATO's policy of transparency and dialogue."
The high-level calls come as the US-led coalition fighting ISIS has observed pro-Syrian regime forces, including Russian private military contractors, once again conducting a slow build-up east of the Euphrates River near where US troops are presently advising local allies.
US Army Col. Ryan Dillon told CNN Tuesday that that the coalition was keeping a close eye on the activity of pro-regime forces and was communicating with their Russian counterparts via the de-confliction hotline to discuss the development.
A US military official told CNN that Russian private military contractors remain in the area and are using local pro-regime troops to scout coalition positions. US officials previously told CNN that Russian private military contractors participated in a pro-regime attack against a US advisers and their local Syrian allies last month, an attack that brought about retaliatory US artillery and airstrikes that killed over 100 enemy fighters. The Russian government later confirmed that Russian citizens were killed in the incident but claimed that they were not working on behalf of the Russian government.
Russia's Defense Minister Sergei Shoigu said Tuesday that Russia was monitoring US and coalition military forces in the region which he said "have become more active in Syria."
"We've always been willing to cooperate with Russia where possible unfortunately they have chosen to be a strategic competitor of late from what happened in the United Kingdom, to what we saw in Ukraine and Crimea," Secretary of Defense James Mattis told reporters at the Pentagon prior to a meeting with his Norwegian counterpart on Tuesday.
"While were open to that. We want stability, We want peace. At the same time, we will defend our democratic institutions and our members of the NATO alliance," Mattis added.