U.S. Chairman of the Joint Chiefs of Staff Mark Milley spoke with Chief of the Russian General Staff Valery Gerasimov by telephone on Thursday.

"The military leaders discussed several security-related issues of concern and agreed to keep the lines of communication open," according to a readout of from Joint Staff spokesperson Dave Butler.

"In accordance with past practice, the specific details of their conversation will be kept private."

It was the first conversation between the generals since Russia began its "special military operation" in Ukraine on February 24.