bracing for impact

Full-scale ground assault against Ukraine likely to begin within hours, U.S. official says

A U.S. official said Wednesday night that the explosions being reported in multiple Ukrainian cities are preliminary bombardments to be followed by a full-scale ground assault, Fox News correspondent Jennifer Griffin reports.

"It's begun," the unidentified official told Griffin, who posted on Twitter that explosions have been heard in the Ukrainian cities of Kyiv, Odessa, and Mariupol. Griffin also wrote that the official told her the Russian ground attack would likely commence after several hours of bombardment and include "all of the full forces Putin has arrayed."

Recent estimates put the number of Russian troops deployed along Ukraine's border at 190,000.

Journalist Babak Taghvaee tweeted that Russia's navy has attacked the port of Odessa and posted a video purportedly showing Russian artillery and rocket barrages directed against the Ukrainian city of Kramatorsk.

Russian President Vladimir Putin announced in a speech early Thursday that he has authorized a military operation in Ukraine after the two Russian-aligned breakaway republics in eastern Ukraine asked him to intervene against the Ukrainian military.

Fighting between separatists and Ukrainian government forces has killed some 14,000 people since it began in 2014. Putin said Russia will now put a final end to that conflict.