Western military analysts believe that Russia cannot, for financial and logistical reasons, keep such units deployed where they are and will have to withdraw them by the summer.
Estimates of the number of new Russian troops moving closer to Ukraine vary from 60,000 to about 100,000, with a US secret service document suggesting that the number could rise to 175,000.
US officials said Russia could attack Ukraine this month, when the country will be tougher, which will facilitate the rapid movement of tanks and other armor.
In talks this week with the United States and NATO, Russia sought security guarantees to alleviate the crisis.
Foreign Minister Sergei Lavrov said on Friday that Moscow was not ready to wait forever for an answer and that he wanted a detailed written response to every Russian proposal.
But what might the Russian attack look like and what could it try to achieve?
“Current deployments are versatile. They leave Russia open, and therefore let the defenders guess, “said Keir Giles, a Chatham House associate.
Here are some possible scenarios.
Heavily armed separatists, backed by Russia, have controlled parts of eastern Ukraine since 2014 and continue to exchange fire with Ukrainian government forces, despite the 2015 ceasefire, which ended the great hostilities.
The conflict in Donbass has killed 15,000 people, says Kiev. Ukraine has long accused Russia of having regular troops in the region, which Moscow denies.
Russia has accused Kiev of harboring plans to recapture the region by force, which Ukraine denies.
A militant of the self-proclaimed Donetsk People’s Republic (DNR) inspects a machine gun in combat positions on the line of separation from the Ukrainian Armed Forces near the insurgent-controlled settlement of Jasne (Jasnoje) in the Donetsk region
In such a feverish atmosphere, there is a greater risk of misunderstanding or unplanned escalation, and Russia could use such an incident as a casus belli.
A source familiar with the Russian Ministry of Defense’s thinking said that this was the most likely scenario if Moscow decided to attack, but he did not know of any such decision. Kiev could also provoke separatists to attack, who could then ask Russia to send troops to help, he said.
Russian forces could expand the fighting in Donbas and draw Ukraine into the conventional conflict, said Neil Melvin, director of international security studies at the RUSI think-tank in London. He said Moscow could try to seize Ukraine’s coastal areas in the Sea of Azov and build a land bridge from the Russian city of Rostov over the Donbass to Crimea, adding: “That would put the Ukrainian government under great pressure.”
ATTACK FROM THE CRIMEA
Russia brought new forces to Crimea, which in 2014 it annexed from Ukraine.
Moscow could launch an attack on Ukraine from the Crimea and seize the territory up to the Dnieper River, which could serve as a natural barrier against any Ukrainian counter-offensive, said Konrad Muzyka, director of the consulting company Rochan, based in Poland.
The operation could begin with artillery, missile and air strikes on Ukrainian troops in the south, and special forces troops could seize bridges and railway junctions, allowing troops and tanks to advance, he said. There are only two roads leading from the Crimea that could be blocked or destroyed, which he said is a potential weakness.
The forces would provide control of the canal, which provided Crimea with fresh water supplies until Russia annexed the region and Ukraine stopped the flow, he said.
A publicly available US Secret Service document said that Russia could invade up to 100 battalion tactical groups (BTG) or about 175,000 troops this month. She said that about 50 BTGs are already located in the north and east of Ukraine and in the Crimea in the south.
The occupation of southern Ukraine could cut Kiev off the coast and NATO’s presence in the Black Sea, Melvin said, and could play well with Russian nationalists, who see the area as a “Novorossiysk” or “New Russia” historic territory.
An attack on multiple fronts could also include a move to the northeast of Ukraine, a siege, but perhaps a non-intrusion into cities, where forces could get stuck in urban fighting. Russian troops could also move to Belarus and open a northern front for Ukraine that would bring Russian forces closer to Kiev, Giles said.
“That, of course, would be the most costly, politically, and human lives, and that’s probably the least likely,” Melvin said of the total invasion.
Military analysts said that even if it defeated the Ukrainian army, which is half its own, Russia could face guerrilla-type resistance, which would make it difficult to maintain captured territory.
CACT ATTACKS OR KYBER ATTACKS
Giles said some scenarios could include long-range missile attacks or cyber attacks targeting critical infrastructure. Missile attacks would take advantage of Ukraine’s weaker missile defenses.
“Different scenarios of how exactly Russia might try to persuade the West to meet its (security) demands by punishing Kiev do not necessarily involve a raid on the country,” he said.
A number of government websites were attacked on Friday. Some displayed a message: ‘Fear and expect the worst.’
Finger of suspicion immediately fell on Russia, although Ukrainian officials said the target was not critical infrastructure.