Ukrainian President Petro Poroshenko said on Thursday he would call on Russian President Vladimir Putin to rein in pro-Russian separatists when the two men meet next week and told the Kremlin chief he had "a strong country, a strong army" behind him.

Poroshenko spoke as government forces, despite taking heavy losses themselves, thrust deeper into rebel-held territory in Ukraine's Russian-speaking east and kept the separatists whom they have battled since April on the back foot.