Russia has surrounded Ukraine on three sides. This is where an invasion could start.

(CNN) — Russia has amassed more than 100,000 troops near Ukraine’s border in recent weeks, according to US estimates, raising fears among Western and Ukrainian intelligence officials that an invasion could be imminent.

As frantic diplomatic efforts are made to avert war, analysts warn that Russia’s military poses an immediate threat to Ukraine.

But if an invasion were to occur, it is unclear where it would start from. Russia has created pressure points on three sides of Ukraine: in Crimea to the south, on the Russian side of the two countries’ border, and in Belarus to the north.

Here are the three fronts Ukraine and the West are watching, and recent Russian moves detected on each.

eastern ukraine

The most attention has been paid to the breakaway regions of Donetsk and Luhansk, where Ukrainian forces and Russian-backed separatists have been in conflict since 2014.

The main assumption of those watching Russian moves is that Moscow could increase the military might it already possesses in the region, thus making eastern Ukraine the easiest position from which to launch an invasion.

Satellite images obtained by CNN show that a large base in Yelnya, which housed tanks, artillery and other weaponry, has been largely emptied, with equipment apparently moving much closer to the border in recent days.

Large amounts of weaponry were moved into the base in late 2021 before disappearing, including some 700 tanks, infantry fighting vehicles and ballistic missile launchers. Social media videos since then show some of that equipment on trains and roads much further south in the Bryansk region, which is close to Ukraine. The weapons and vehicles are from the same units that had previously been positioned at Yelnya.

Stephen Wood, a senior director at satellite imaging company Maxar, told CNN: “It seems to me that a considerable number of vehicles [tanques, artillería autopropulsada y otros vehículos de apoyo] they have departed from the northeast vehicle park; Additional armored vehicles departed from the most central car park.”

Meanwhile, increased activity in the Kursk and Belgorod oblasts, which border northeastern Ukraine, add to the concerns.

“We observed a massive influx of vehicles and personnel in Kursk,” Konrad Muzyka, an expert in tracking military movements at Rochan Consulting, warned on Twitter.

Phillip Karber of the Potomac Foundation in Washington, who has also studied Russian troop movements in detail, told CNN this month: “Russia’s strongest offensive formation, the First Guards Tank Army, which normally is stationed in the Moscow area, has moved 400 kilometers to the south and is gathering in the optimal area for a rapid armored offensive on the Khursk-Kyiv invasion route.”

Belarus

Concern has also been raised about a large buildup of Russian soldiers in Belarus, a country closely allied with Moscow that could provide another way into Ukraine.

Russia and Belarus started on Thursday 10 days of joint military exercisesthe size and timing of which have raised fears in the West.

Moscow’s deployment to Belarus is believed to be the largest there since the Cold War, with “some 30,000 expected combat troops, Spetsnaz special operations forces, fighter jets including SU-35s, Iskander dual-capable missiles and S-400 air defense,” according to NATO Secretary General Jens Stoltenberg on February 3.

It is also the largest exercise the Belarusian armed forces have conducted at any time of the year, according to the Center for Strategic and International Studies (CSIS). The Russian Defense Ministry claimed that the purpose of the drills, called “Allied Resolution-2022”, included repelling “external aggression”.

Some fear the buildup points to a Russian plan to advance on Kyiv from the north. A European diplomat told CNN earlier this month that the concentration of forces is a “big, big concern,” noting that this would be the missing piece Moscow would need to launch a swift attack on the Ukrainian capital.

The joint drills would also provide cover for an outflanking movement through Belarus and into northern Ukraine, CSIS warns.

And satellite images released by Maxar appear to show that Russia’s military has advanced deployments in various locations in Belarus. The deployments are likely related to the joint exercises, but other photos show camps being set up near the Ukrainian border, hundreds of kilometers from where the exercises are taking place.

However, if Russia were to focus on the Belarusian border as a point of entry into Ukraine, the route would be fraught with difficulties.

The Russian soldiers would have to negotiate the Pinsk swamps, also known as the Pripet swamps, one of the largest wetlands in Europe, which straddles the border between Belarus and Ukraine, a dense, flooded and heavily forested terrain. which extends over 269,359 square kilometers.

That region obstructed Nazi forces during Operation Barbarossa, the doomed German invasion of the Soviet Union, in 1941.

According to the Institute for the Study of Warfare, “Swamps can be difficult, in some places probably impossible, for mechanized forces to traverse when wet.”

crimea

The peninsula annexed by Russia in 2014 would provide a natural setting for any new operation, but it is unclear whether Moscow would attempt to launch a move into Ukraine from Crimea.

Maxar has seen a large deployment of troops and equipment. He assesses that more than 550 troop tents and hundreds of vehicles have arrived north of the Crimean capital Simferopol.

Maxar then identified for the first time on Thursday a new deployment near the town of Slavne on the northwestern coast of Crimea, which included armored vehicles.

Those new deployments were seen on the same day that several Russian warships arrived in Sevastopol, Crimea’s main port. The Russian Defense Ministry released images Thursday of six large amphibious assault ships in port.

The Ukrainian Navy responded that “Russia continues to militarize the Black Sea region, transferring amphibious assault ships to put pressure on Ukraine and the world.”

Ukraine’s naval forces “are ready for the development of any scenario and provocation, to defend the country from the sea,” he added.

Any move south from Ukraine could be aided by troops in Transnistria, the Russian-backed breakaway region of Moldova, where a buildup has also been reported.

CSIS analysts say Russian troops could attempt a coup in Odessa, a Ukrainian port city northwest of Crimea, “by sailing their amphibious ships directly to the port of Odessa and moving directly into the city.”

He calls such a move “a high-profit but also high-risk trade.” Odessa is a highly populated city and urban combat there would favor those defending it, while Russian forces would have to eliminate Ukraine’s air defenses and then join forces arriving from the east of the country.

CNN’s Tim Lister, Gianluca Mezzofiore and Olga Voitovych contributed to this report.