Ukraine's President Petro Poroshenko, wearing a white helmet and an oxygen mask, waves as he sits in an MIG-29 fighter jet before his flight at an air military base in Vasylkiv close to capital Kiev, Ukraine, Saturday, Aug. 5, 2017 during Air Force day celebrations. (AP Photo/Mykhailo Markiv, Presidential Press Service Pool Photo via AP)

Women drummers perform at a police anniversary ceremony in front of St. Sophia Cathedral in central Kiev, Ukraine, Friday, Aug. 4, 2017. Ukraine's National Police marks the second year since it was founded. (AP Photo/Efrem Lukatsky)

Policewomen drummers perform at a police anniversary ceremony on Sophievska square in central Kiev, Ukraine, Friday, Aug. 4, 2017. Ukraine's National Police are marking the second year since it was founded. (AP Photo/Efrem Lukatsky)

Ukraine's President Petro Poroshenko holds 4-year old Gleb Khurtepa, in a medical mask and police uniform, as he helps him take a seat on a police motorbike at a ceremony on Sophievska square in central Kiev, Ukraine, Friday, Aug. 4, 2017. Khurtepa is suffering from cancer. His dream is to become a policeman. Ukraine's National Police are marking the second year since it was founded. (AP Photo/Efrem Lukatsky)

Ukraine's President Petro Poroshenko, hand in hand with 4-year old Gleb Khurtepa, a boy in a medical mask and police uniform, approach a police motorbike at a ceremony on Sophievska square in central Kiev, Ukraine, Friday, Aug. 4, 2017. Khurtepa is suffering from cancer. His dream is to become a policeman. Ukraine's National Police are marking the second year since it was founded. (AP Photo/Efrem Lukatsky)

Women police unit prior to a police anniversary ceremony on Sophievska square in central Kiev, Ukraine, Friday, Aug. 4, 2017. Ukraine's National Police marks the second year since it has been founded. (AP Photo/Efrem Lukatsky)

A women police unit officer, ear-rings in Ukraine's national colours, prior to a police anniversary ceremony on Sophievska square in central Kiev, Ukraine, Friday, Aug. 4, 2017. Ukraine's National Police marks the second year since it has been founded. (AP Photo/Efrem Lukatsky)

Special police unit officers at a police anniversary ceremony on Sophievska square in central Kiev, Ukraine, Friday, Aug. 4, 2017. Ukraine's National Police marks the second year since it has been founded. (AP Photo/Efrem Lukatsky)