"Per agreement with Russia, the MOU will not be released publicly. It will be shared with Coalition partners," Baldanza said of the document signed by US and Russian officials on Tuesday.
Earlier on Tuesday, Pentagon Press Secretary Peter Cook told reporters that the MOU has not been made fully public at the request of Russia.
The MOU seeks to prevent air incidents between Russian and US aircraft, including drones, which operate in the Syrian airspace.
A US-led coalition of 62 nations has been bombing ISIL targets in Syria since September 2014, but without the approval of UN Security Council or the Syrian government.
Since September 30, Russia has conducted an airstrikes campaign against ISIL targets in Syria at request of Syrian President Bashar Assad.
