Ukraine's top security official announced Wednesday that a nationwide state of emergency will be declared due to the threat of a Russian invasion.

The declaration must be approved by the Ukrainian parliament before the state of emergency can go into effect for an initial 30 days. The move, which differs from the introduction of martial law, would allow local authorities across the country of 41 million people to put restrictions and heightened security measures in place, such as curfews and limits on movement.

Oleksiy Danilov, secretary of Ukraine's National Security and Defense Council, said the state of emergency would be a "preventative" measure "so that the country preserves its calm, so that our economy works and our country works." Any restrictions imposed under the declaration would likely vary from region to region, according to Danilov.

"Depending on situation on the ground in a particular area, the local bodies can impose various measures including curfews, only if needed," Danilov told reporters during a press conference in Kyiv on Wednesday. "We won't make people suffer unnecessarily, but we must insure people's safety."

He then gave examples of what those restrictions could be: "It can the reinforcing of security around public order and critical infrastructure facilities. It can be certain limits imposed of the movement of transport. It can mean additional vigilance. It can be the checking of various documents for people."

Danilov noted that the state of emergency would be imposed on all of Ukraine's territory except for the eastern regions of Donetsk and Lugansk because a special emergency status has been in place there since 2014, when pro-Russian separatists took control of some areas.

-ABC News' Patrick Reevell

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