Russia-Ukraine updates: US to ban Russian carriers from its airspace

One of Ukraine's far-right volunteer battalions announced Wednesday it is mobilizing to prepare to fight, amid fears of an imminent Russian invasion.

During Russia's first invasion in 2014, the Ukrainian army was in disarray, prompting civilians to form volunteer battalions -- many of them with right-wing ideologies. These highly motivated private armies -- some funded by oligarchs -- helped stem the fall of eastern Ukraine to Russia-backed separatists.

But once large-scale fighting had ended, the Ukrainian government moved the volunteer battalions back from the front line because they were seen as potentially provocative and problematic.

The so-called Right Sector is one of Ukraine's most famous volunteer battalions. It's made up of radical nationalists who played a crucial role in the 2014 revolution. In Russia, the group was made into a propaganda boogeyman.

The Right Sector's return to the front line in eastern Ukraine will be used heavily by Russian propaganda. But it also shows how worried Ukrainians are getting, especially if more volunteer battalions start mobilizing.

In a Facebook post Wednesday, Right Sector said it is mobilizing its "assault brigade" due to the "high probability of the start of a full-scale invasion by the Russian army."

"Our unit has already defended Ukrainian independence for 8 years from the occupiers," the group said. "In the case of a full scale invasion we, as always, will be at the front of the fight."

-ABC News' Patrick Reevell

The Russian Ministry of Defense claimed Wednesday that 100,000 refugees from two Russia-backed separatist areas in eastern Ukraine have arrived across the border in Russia.

The claim was unverified and highly improbable, as it appeared to be part of Russia's intensifying efforts to spin an image of a major humanitarian crisis in the region to build a pretext for a possible invasion.

Russia-backed separatists have forced civilians living in the areas to evacuate despite the fact that there is no increased threat from the Ukrainian military. While thousands of people have been bused out of the region to Russia, the alleged figure of 100,000 appeared vastly exaggerated.

Russia's claims have been accompanied by a barrage of false stories and staged videos of alleged attacks by Ukrainian forces, all of which have been blaring across Russian state media in recent days.

-ABC News' Patrick Reevell

Russian-controlled separatists are claiming two large “terrorist attacks” took place in their territory Tuesday night, as the separatists and Russia continue to intensify their efforts to create a pretext for a possible Russian attack.

The separatists claimed explosions went off at a TV tower and near a trolley bus depot, and they released video afterward they claim shows emergency workers looking at damage.

The claims are highly suspect, and they came amid a barrage of fake reports of supposed Ukrainian attacks that are being swiftly debunked.

The claims also came as Ukraine released video showing heavy artillery fire from separatists hitting a village called Chastiya -- which means “happiness” -- on the Ukrainian side of the frontline. The video appears to show rockets striking a house.

Artillery fire also hit a power station nearby yesterday.

It appears the Russian-controlled separatists have intensified their fire onto Ukrainian positions in the hope of stoking return fire and creating an impression of a general escalation.

-ABC News’ Patrick Reevell

Daleep Singh, the White House's top national security official crafting sanctions, spoke to reporters about the administration's sanctions against Russians and hinted that this is only the beginning of the United States' plan to defend Ukraine.

"If Putin escalates further, we will escalate further, using financial sanctions and export controls," Singh said.

Singh claimed the sanctions will only hurt the Russian economy.

"None of our measures are designed to disrupt the flow of energy to global markets. And we are now executing a plan in coordination with major oil producers and major oil consumers to secure the stability of global energy supplies," he said.

When asked by ABC News’ Cecilia Vega what it will take to target Putin personally, Singh said he wouldn’t say “exactly what it would take” but added that “no option is off the table.”

-ABC News' Ben Gittleson