"The US asked us to keep these additional issues in secret so far. We are keeping the promise. We will see how the situation will develop given some parties to the negotiations are not aware of the details" Ushakov told reporters.
If the new ceasefire in Syria lasts for seven days, Russia and the United States will work together to establish a Joint Implementation Center and carry out joint airstrikes against terrorists in the war-torn country.
On Friday, Lavrov told Kerry in a phone call that the entire package of the US-Russian agreements on Syria should be made public.