NATO's secretary-general is insisting international observers be given the freedom of movement and the protection they need to monitor the cease-fire in Ukraine.

Jens Stoltenberg said Wednesday that if monitors from the Organization for Security and Cooperation in Europe are not provided with what they need to work, there can be no certainty how many heavy weapons are being moved or where they have been transported to.

NATO's top civilian official says there is still a Russian presence in Ukraine's east, including delivery of weapons and strong support for local pro-Moscow separatists.

Ukraine's president said Tuesday that government and rebel forces have pulled back most of their heavy weapons in the east, but each side accused the other of stalling on complying with other terms of a cease-fire deal.