"U.S. President Barack Obama has vetoed the bill on the budget in support of the U.S. national defense for 2016 due to a number of reasons not related to the volume of assistance to Ukraine, which is envisaged in this document," the Ukrainian Embassy said on its website.
According to this information, Obama has explained his decision by the fact that Congress has ignored a number of reforms to modernize the U.S. Army which were proposed by the presidential administration as well as the fact that the document makes it impossible to close Guantanamo Bay prison, which is a matter of principle for the U.S. president.