The Pentagon spokesman says Russia and the United States have signed an agreement to minimize the risk of incidents as both countries carry out airstrikes in Syria. 

Spokesman Peter Cook says the agreement was signed on Tuesday. Although he says the Russian government insisted that the text of the agreement remain secret, it lays out safety protocols, specifies which frequencies both sides should use to communicate, sets up a hotline on the ground and establishes a working group to talk out further issues. 

Cook says the agreement does not include zones of cooperation or sharing of target information. 

Russia began flying bombing missions in cooperation with the Syrian government earlier this month. The U.S. leads an international coalition that is conducting airstrikes against Islamic State targets in Syria.