"It's safe to say you have over a million people now displaced as a result of the conflict, internally and externally together," Vincent Cochetel, director of the UNHCR's bureau for Europe, told reporters in Geneva.
He said that the number of people displaced inside Ukraine had more than doubled in the past four weeks and reached 260,000 people.
He said that the actual number of people displaced could be higher as many are staying with families and friends and choose not to register with the authorities.
"If this crisis is not quickly stopped, it will have not only devastating humanitarian consequences but it also has the potential to destabilize the whole region," Cochetel said.
According to the UNHCR, a total of 4,106 Ukrainians requested asylum in the European Union between January and July, compared to 903 applications in 2013. Most Ukrainian applications for asylum were in Poland (1,082), Germany (556) and Sweden (500). In addition, 380 Ukrainians have sought asylum in Belarus.