KRAMATORSK, Ukraine — A Ukrainian soldier brought his officers' sword home in 1918 after fighting alongside the Russians in the first World War, and it's now proudly displayed in the Palchenko family's modest home in this small city in the country's east. Alexander Palchenko, 56, is the grandson of that soldier and a former Soviet reserve officer himself. With Russian forces massed just across the nearby border, he'd been thinking hard about his family's long military history lately — and about how he would need to continue it if those troops invaded, taking up arms against his former ally. "Look at my father," he said, pointing to a portrait of a uniformed man from World War II. "With such a father, how could I react in any other way?"

Worries of a Russian invasion are gripping eastern Ukraine, as some residents worry that their neighbor's seizure of Crimea may be only a prelude to a bid to grab more territory. The government in Kiev has rushed forces to the border and started mobilizing reserves and a national guard. But many of its supporters in the region believe these measures would do little to stop a determined Russian advance.

Instead, some locals say they're readying themselves for what they call a "partisan war" — or guerilla war — against their far more powerful enemy.

The Palchenko household counted itself enthusiastically among these ranks. Asked how many of their neighbors supported the idea, Olga, Alexander's prim and amiable wife, made a fierce chopping motion with her hand: "All of them."

Russia boasts many supporters in the Donetsk region, where Kramatorsk lies, and many more would be too afraid to join the fight — making Olga Palchenko's assessment far too optimistic. But sentiments for taking up arms among some residents around the region seemed very real, and some said they were already organizing themselves for the fight.

Sitting at the family's computer, Alexey Palchenko, 28, said many of his friends had bought guns recently, and he pulled up an article he'd found the day before on a local version of Facebook. Complete with diagrams and lessons on urban warfare from Chechnya, it was titled: "How to destroy a Russian tank."

More formal efforts were underway — Alexey Palchenko was a member of a local group that claimed about 50 men, and said they'd organized themselves for "self-defense."

The group's leader, Vladimir Tkachuk, 42, said he'd made an "evacuation plan" with his family, whom he planned to rush to Kiev in the event of an invasion. He'd then return quickly to Donetsk, he said: "Our organization will go underground, and we will fight."

A former Soviet ranger who fought in Tajikistan in the early 1990s, Tkachuk had returned from war to become a pastor, and he led a small Pentecostal congregation in the city. He and other locals had organized themselves during this winter's protests in Kiev, first as medics and then as guards. He was still unsure how they would find the weapons, he said, but was hopeful they and groups like them could make life hard on the Russians if they came to Donetsk. "We understand that the Ukrainian army is much weaker than the Russian army. But if we speak about partisan war, it's a horrible thing, and they must know it," he said. "This is not Crimea."

Others around Donetsk also said they were organizing. In the city of Gorlovka, Igor Slavgorodskiy, the Donetsk head of a powerful far-right political party called Svoboda, said he had organized local cells and secret gathering points around the city. He wouldn't say how many men he had — hundreds, he claimed, though his reaction suggested the true figure might be lower. He said many more would surface if an invasion took place. They had gathered "some quantity of legal weapons," he added, but needed more. "If the invasion happens, we are ready to face them," he said. "How do we react to occupiers? We struggle against them. I don't think we meet them with flowers."

On Tuesday afternoon, Russian President Vladimir Putin formally announced the annexation of Crimea. He also sounded the most combative rhetoric of his presidency — ratcheting up fears, despite claiming otherwise, that he might turn his sights next on Ukraine's east.

Russia has already massed troops on the border for what it claims are training exercises, while invoking the right to protect Russian-speaking people across Ukraine, the same justification it used for seizing Crimea. Recent pro-Russia protests in eastern cities like Donetsk have been seen by some residents as a possible precursor to Russian intervention — which was the stated aim of many of the protesters themselves.

On Monday, Anders Fogh Rasmussen, NATO's secretary-general, told CNN that he saw a "clear risk" of Russian intervention in eastern Ukraine. "I don't see any de-escalation. On the contrary, I see Russian military build-up, and this is a matter of concern," he said.

Residents and observers alike warn that eastern Ukraine is a far cry from Crimea, where Russia's existing military presence and sympathies from the majority ethnic-Russian population helped it overtake the peninsula bloodlessly. Whatever Russia's support may be in the east, an invasion would also bring it considerable antipathy — and potentially pave the way for a long and bloody conflict.

One senior U.S. official tracking the crisis told BuzzFeed that regardless of the outcome in Crimea, "what [Putin] really wants is control over Kiev and over the entire country."

"I don't rule out that he will send in troops" to the east, the official added. "But if he does that, it will be civil war. And it will be bloody and long, and it will be something that the majority of Russians do not support."

Despite the talk of resistance, some of Russia's opponents in the region believe there is little to be done to stop a Russian advance. One activist in the city of Kharkiv, seen by many as the likely first target of any Russian incursion, said "the only protests would be in kitchens. The region would surrender."

Asked what his own reaction to a Russian invasion would be, he said: "I will drink Jack Daniels — or vodka."

Another anti-Russia activist in Kramatorsk said he'd been one of the first in the city to sign up for the national guard and that he would find a weapon and join the so-called partisan war if one did erupt. But he didn't hold out much hope. "I really don't think we're ready to make a serious defense here — we have no petrol, no equipment, and no weapons," he said.

Other residents said they were quietly arming up simply for their own self-defense, fearful that security would quickly deteriorate if an invasion took place. One local investor who declined to be identified said he had been shopping on the area's considerable black market — fueled by its massive stockpiles of Soviet-era weapons, many of which are believed to have leaked out from the military-run stores thanks to two decades of rampant corruption — for illegal weapons. He listed a long range of guns on the market: from Makarov pistols to Kalashnikovs. He had recently purchased a modified version of an AK-47. "I need weapons not for war with the Russian army, but to protect myself and my family from the criminals that would rise up in that situation," he said.

Talk of partisan war could be rooted at least in part on wishful thinking — and also on attempts to project strength amid a raging information war. Many of those who say they are organizing, likewise, may not be the ones who end up following through on the threat.

But one veteran of the Soviet Afghan war who has organized his own "self-defense" group in Donetsk city and who has been advising the newly appointed governor on security, said that in the event of a Russian invasion, it was natural to expect that war would take that course. "Partisan war will come to Donetsk in that case — 100%," the man, a former fighter pilot named Roman Svitan, said.

It would be the line of defense against a far more powerful enemy, he added. "If any when you manage to kill that first enemy from the other side, then you have your first weapon. And three people might die to get that weapon, but that fourth man who gets the weapon, will also get a lot of experience," he said. "If the war comes here, a lot of blood will be shed."

On Monday night, in another small city in Donetsk, one 30-year-old man popped the trunk of his car to show one of the weapons he and his friends had gathered in their own bid at forming a local defense group. It was a small hunting rifle, kept in a dusty leather case. "We need weapons," he said, "and a leader to organize."