NATO Secretary-General Jens Stoltenberg has called on Russia to withdraw heavy weapons from eastern Ukraine.
Stoltenberg was speaking to reporters near the western Ukrainian city of Lviv on September 21.
He said the drop in fighting between Ukrainian government forces and Russian-backed rebels since the start of September was encouraging, but described the situation as "very fragile."
"Russia continues to support the separatists and provide them with weapons, with different kinds of equipment, with training, with forces," he said.
Kyiv and the West say Russia has sent troops and weapons to fuel the separatist conflict that has killed more than 7,900 people in Ukraine's east since April 2014. Russia denies the charges.
Stoltenberg started a two-day visit on September 21, his first trip to Ukraine as NATO chief, in a show of support for Kyiv's pro-Western government.