Images of Russian troops along the border with Ukraine. Military hardware moving along the bridge to the Russian-occupied Crimea. Concerned statements by NATO and a U.S. president who assures his Ukrainian counterpart that Ukraine is not alone.

"[I]s Russia "preparing a new stage in the war against Ukraine?" Süddeutsche Zeitung wrote.

"The most optimistic answer: Russian President Vladimir Putin is only flexing his muscles to test US President Joe Biden and also punishing Kyiv for a recent crackdown on Putin's close confidant. Option two: Putin seeks military confrontation in order to officially station Russian soldiers as "peacekeepers" in the Russian puppet republics in Donetsk and Luhansk. Scenario three: The Kremlin is preparing military action to conquer a land corridor through Ukraine to Moscow-occupied Crimea and thus secure the precarious water supply to the peninsula that has been turned into a Russian military fortress.

Military escalation unfolded amid Russian Foreign Minister Sergei Lavrov's comment about Russia-West relations being at their "lowest point". The EU imposed new sanctions on Russia after the attack on opposition figure Alexei Navalny. In February, Ukrainian President Volodymyr Zelensky took action in Kyiv against a local oligarch Viktor Medvedchuk, who is close to Putin. Zelensky switched off TV channels controlled by Medvedchuk and froze his other assets.

Read alsoRussia pulling military hardware toward Ukraine border: Videos show trucks with covered license plates (Video)U.S. President Joe Biden said on ABC that he saw Putin as a "killer". Russia's president, he said, would also pay a price for his interference in the previous presidential campaign in favor of Donald Trump. The Russian president immediately ordered the Russian ambassador back to Moscow – a sharp step in diplomatic protocol.

But that was not Putin's only answer. Four days after Biden's "killer" interview, Putin called in Defense Minister Sergei Shoigu. Another four days later, Shoigu announced that the 56th Air Assault Brigade (an estimated 4,000 soldiers) would be relocated to Crimea. The next day a fierce battle followed near the Ukrainian village of Shumy in Donbas.

After Moscow this February announced exercises in Crimea involving thousands of paratroopers to practice a territorial grab in, military analysts speculated that Moscow might be planning to force a land corridor through Ukraine to Crimea in order to regain control of freshwater supplies to the drying-out peninsula. Seizing such a land corridor would, of course, be a major act of war.

At the moment, however, not even those Ukrainians who often publicly raise alarm, believe this could happen. Commander Khomchak said on Ukrainian television that the General Staff did not believe in an imminent war.

It is more likely that Putin is preparing a possible dispatch of Russian "peacekeeping troops" to Donbas in order to officially expand control – a preliminary step to a further annexation of eastern Ukraine. Several representatives of the "Nororossiya" ideology, which Putin himself supported, have been pleading for this for years. Since April 2019, Putin has illegally issued Russian passports to the residents of Donbas – according to the Eastern Human Rights Group, a good 442,000 Russian passports had been by January.

Read alsoBiden affirms U.S. support for Ukraine in face of Russian aggression – White HouseOn January 28, the conference entitled "Russian Donbas" was held in the occupied Donetsk. The star guest was Margarita Simonyan, head of the Kremlin propaganda TV channel Russia Today. Her message: "The people of Donbas want to live at home and be part of our great homeland. And we have a duty to take care of them. Mother Russia, bring Donbas home!" Simonyan's appearance is unlikely to have come about without the green light from the Kremlin. Officially, Kremlin spokesman Dmitry Peskov assured that the annexation of Donbas was "not on the agenda".

At this point in time, it would be more plausible than an Anschluss for Russia to deploy "peacekeepers", authors suggest. "In view of the Minsk Agreement signed in 2015, which officially binds Moscow, Putin needs an excuse for their use to allegedly ensure "security" for Russian speakers.

"Putin's video conference with [German Chancellor Angela] Merkel and French President Emmanuel Macron on March 30 indicated he was looking for such excuse," the report reads.

That's because Putin during the conference complained that Ukraine was allegedly plotting provocations on the contact line.