TOPSHOT - This handout picture taken and released on November 28, 2018 by the Ukrainian Presidential Press service shows the President Petro Poroshenko talking with tankmen during drills near the city of Chernihiv, northern Ukraine. - Ukraine's president imposes martial law in border regions on November 28, 2018 for 30 days in 10 regions bordering Russia, the Black Sea and the Azov Sea. (Photo by MYKOLA LAZARENKO / UKRAINIAN PRESIDENTIAL PRESS SERVICE / AFP) / RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT "AFP PHOTO / UKRAINIAN PRESIDENTIAL PRESS SERVICE" - NO MARKETING NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS ---

Ukrainian servicemen attend a military training in Chernihiv region, Ukraine, Wednesday, Nov, 28, 2018. Russia and Ukraine traded blame after Russian border guards on Sunday opened fire on three Ukrainian navy vessels and eventually seized them and their crews. The incident put the two countries on war footing and raised international concern. (Mykola Lazarenko, Presidential Press Service via AP)

Ukrainian President Petro Poroshenko, second from right, speak with soldiers during a military training at a military base in Chernihiv region, Ukraine, Wednesday, Nov, 28, 2018. Russia and Ukraine traded blame after Russian border guards on Sunday opened fire on three Ukrainian navy vessels and eventually seized them and their crews. The incident put the two countries on war footing and raised international concern. (Mykola Lazarenko, Presidential Press Service via AP)

Ukrainian President Petro Poroshenko speak to soldiers during a visit to a military base in Chernihiv region, Ukraine, Wednesday, Nov, 28, 2018. Russia and Ukraine traded blame after Russian border guards on Sunday opened fire on three Ukrainian navy vessels and eventually seized them and their crews. The incident put the two countries on war footing and raised international concern. (Mykola Lazarenko, Presidential Press Service via AP)

This handout picture taken and released on November 28, 2018 by the Ukrainian Presidential Press service shows the President Petro Poroshenko talking with tankmen during drills near the city of Chernihiv, northern Ukraine. - Ukraine's president imposes martial law in border regions on November 28, 2018 for 30 days in 10 regions bordering Russia, the Black Sea and the Azov Sea. (Photo by MYKOLA LAZARENKO / UKRAINIAN PRESIDENTIAL PRESS SERVICE / AFP) / RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT "AFP PHOTO / UKRAINIAN PRESIDENTIAL PRESS SERVICE" - NO MARKETING NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS ---

This handout picture taken and released on November 28, 2018 by the Ukrainian Presidential Press service shows the President Petro Poroshenko talking with tankmen during drills near the city of Chernihiv, northern Ukraine. - Ukraine's president imposes martial law in border regions on November 28, 2018 for 30 days in 10 regions bordering Russia, the Black Sea and the Azov Sea. (Photo by MYKOLA LAZARENKO / UKRAINIAN PRESIDENTIAL PRESS SERVICE / AFP) / RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT "AFP PHOTO / UKRAINIAN PRESIDENTIAL PRESS SERVICE" - NO MARKETING NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS ---

This handout picture taken and released on November 28, 2018 by the Ukrainian Presidential Press service shows the President Petro Poroshenko talking with tankmen during drills near the city of Chernihiv, northern Ukraine. - Ukraine's president imposes martial law in border regions on November 28, 2018 for 30 days in 10 regions bordering Russia, the Black Sea and the Azov Sea. (Photo by MYKOLA LAZARENKO / UKRAINIAN PRESIDENTIAL PRESS SERVICE / AFP) / RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT "AFP PHOTO / UKRAINIAN PRESIDENTIAL PRESS SERVICE" - NO MARKETING NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS ---