Russia has denied allegations that it has sent weapons inside Ukraine. Jim Sciutto reports.
Ukraine prepares for fighting as Russian forces move weapons and troops into the country. Jim Sciutto reports.
CNN's Jim Sciutto reports on the collapsing ceasefire between Ukraine and pro-Russian separatists. Full story
Accusations Russia behind new Ukraine violence
Wolf Blitzer talks to Daniel Baer, U.S. Amb. to Org. for Sec. & Cooperation in Europe about the recent violence in the region.
Army Chief of Staff Gen. Ray Odierno tells Wolf Blitzer that Russia flying planes without any communication is 'concerning'. Full story
Unusual Russian flights concern NATO
An unusual uptick in the size and scale of Russian flights in European airspace has raised concerns for NATO officials.
Wolf Blitzer talks to Rear Admiral John Kirby about the severity of U.S. and Canadian jets intercepting Russian planes.
U.S. officials say 1,000 Russian troops have entered Ukraine as Ukrainian military slam Russia for a "full-scale invasion." CNN's Barbara Starr reports.
The battle for eastern Ukraine continues to rage on as government forces push further against pro-Russian separatists. CNN's Nick Paton Walsh reports on the ongoing violence - as Russia masses more troops on the border.
U.S. officials say they have observed Ukrainian forces firing short-range missiles near pro-Russian rebel positions. CNN's Barbara Starr reports.