NATO chief Jens Stoltenberg says Russia and pro-Moscow rebels in eastern Ukraine now have the capacity to launch new attacks "with very little warning" after a sustained military buildup.
Stoltenberg told journalists in Brussels, "In eastern Ukraine, Russia and the separatists [now] have capabilities which enable them to launch new attacks with very little warning time."
Stoltenberg said the situation in eastern Ukraine is headed "in the wrong direction" despite a cease-fire agreement reached in February.
"We see more loss of life, a rise in cease-fire violations, obstruction of the monitors, and continued Russian support for the separatists. This is a disturbing trend in the wrong direction," he said.
NATO foreign ministers are due to discuss the situation in Ukraine later this week, when they will meet in the Turkish city of Antalya.
The talks will also touch upon "the strategic implications of a more assertive Russia," Stoltenberg said.
Based on reporting by dpa and AFP