NATO's top general said Saturday the two-week-old truce between Ukraine and pro-Russian militants fighting in the country's east is a "cease-fire in name only," and he said that by enabling a free flow of weapons and fighters across the border Russia has made it nearly impossible to determine how many of its troops are operating inside Ukraine.

U.S. Air Force Gen. Philip Breedlove, the Supreme Allied Commander Europe, told a news conference after meeting with NATO military chiefs that he is hopeful about Saturday's announced agreement for creation of a buffer zone between Ukrainian and pro-Russian forces.

The deal reached by representatives of Ukraine, Russia, the Moscow-backed rebels and the Organization for Security and Cooperation in Europe marks an effort to add substance to the Sept. 5 cease-fire agreement that has been frequently broken by clashes.

Breedlove has put the main blame on Russia for the continuing conflict, which has killed an estimated 3,000 people in eastern Ukraine since April. 

"So the situation in Ukraine is not good right now," he said. "Basically we have a cease-fire in name only."

Breedlove said violence levels in Ukraine, including the number of artillery rounds fired in the past few days, are as high as prior to the cease-fire. The general added that Russian forces are still operating inside eastern Ukraine but numbers cannot be pinpointed.

"Right now the border is being maintained open by Russian forces and Russian-backed forces, and the fluidity of movement of Russian forces and Russian-backed forces back and forth across that border makes it almost impossible to understand the numbers," he said.

He said it is clear that the number of Russian troops in Ukraine has declined significantly over the past week or so, with some returning to the Russian side of the border — "which is good, except that they haven't returned home and are still available to bring their military force to bear on Ukraine, should it be desired" by Russian government leaders.

Neither Russia nor Ukraine is a member of NATO, but both share borders with NATO-member countries. Recent Russian military behavior, including its annexation of the Crimea Peninsula of southern Ukraine earlier this year, is a major worry inside the U.S.-led alliance. Moscow has repeatedly denied sending troops into Ukraine, as well as accusations from Kiev that it is arming and training the separatists. 

Breedlove said the Vilnius meeting discussed the proposed creation of a new rapid reaction corps that could deploy several thousand allied combat troops on short notice anywhere in eastern Europe. The plan, announced in its broad outlines at a NATO summit meeting earlier this month in Wales, is part of the West's response to Russia's recent moves against Ukraine. Basic details, however, such as how troop contributions to the force would be shared by individual NATO member countries have yet to be worked out.

The Associated Press contributed to this report.