With approximately 100,000 Russian troops stationed near the Ukrainian border, warships stationed in the nearby Black Sea, and Russian tanks pouring in from the north, fears that Russian President Vladimir Putin is preparing to launch an invasion continue to grow within the former Soviet republic and among NATO allies.

On Friday, Ukrainian President Volodymyr Zelensky shocked the world by declaring that he had “received information that a coup d’état will take place in our country.” It could happen as soon as Wednesday or Thursday of this week, according to Zelensky.

Zelensky did not accuse the Kremlin of plotting to destabilize his government, but he did say that taped conversations suggest the possible involvement of Rinat Akhmetov, a Moscow-connected oligarch in Ukraine who controls much of the country’s media and coal resources. Ahkmetov has vehemently denied any involvement in the alleged coup, but some Ukrainians, including investigative journalist and former parliamentarian Serhiy Leshchenko, believe he is actively conspiring with Putin to weaken Ukraine.

Analysts disagree on what is causing Ukraine’s rocky internal politics, where Zelensky’s approval ratings have been falling as he attempts to limit oligarchs’ media power and political clout, but there is widespread concern about Russia’s military buildup.

The conflict also demonstrates the potential for attracting other nations. Belarus, a close Kremlin ally, announced Monday that it would participate in joint military exercises with Russia near its southern border with Ukraine. According to Gustav Gressel, a senior fellow at the European Council on Foreign Relations who has been closely tracking troop movements, Russian troops have already arrived. More Russian troops are joining those already stationed in occupied Crimea, he says.

NATO has troops stationed in Latvia, Lithuania, Estonia, and Poland, as well as ships cruising the Baltic Sea, in response to Russia’s military buildup on Ukraine’s doorstep, which is seen as preparation for a possible incursion. NATO Secretary General Jens Stoltenberg told reporters at a press conference in Latvia on Monday that “Russia has amassed a large and unusual concentration of forces in this region,” moves that NATO considered “unprovoked and unexplained.”

The latest moves, a repeat of military actions Russia took in March, as well as other Putin-linked geopolitical fires across the region, are putting the Western alliance, the European Union, and the United States to the test. Putin continues to maintain that Ukraine is linked to Russia by both history and race.

Former US Ambassador to Ukraine John Herbst, now senior director of the Atlantic Council’s Eurasia Center, believes Russia’s display of military might is motivated in part by Moscow’s concerns about Ukraine’s attempts to join NATO and the EU.

Herbst believes Putin is mostly bluffing, attempting to persuade Ukraine to grant autonomy and veto power to its mineral-rich eastern regions, where Russia has been funding a covert proxy war that has killed over 13,000 people since 2014. He does not, however, rule out a full-fledged assault.

Herbst, who supports increased American military assistance to Ukraine, applauds the Biden administration’s recent moves, such as dispatching diplomats to Moscow and issuing public warnings to Putin from Secretary of State Antony Blinken, as well as convening meetings with Europeans to discuss possible sanctions. However, he believes the administration made a serious mistake earlier this year when it lifted congressionally imposed sanctions on Nord Stream 2, Russia’s new natural gas pipeline that connects its gas fields to Germany.

Herbst noted that the agreement allowed Russia to discontinue use of the Ukrainian pipeline, which had previously been the most heavily used by Gazprom, Russia’s state-owned energy corporation. Allowing the completion of NS2 has given “Putin an ace,” allowing him to further manipulate gas supplies to Europe, which is already in a vulnerable position due to its reliance on Russian gas.

Putin, who appears to be allying with China — both countries recently participated in war games off the coast of Taiwan — is demonstrating that he will not simply accept Western demands. He is attempting to manipulate Russian gas supplies to Europe during a shortage caused, in part, by Gazprom’s refusal to fill its gas storage tanks in Western Europe.

Not only does Putin appear to be cutting gas and coal to Ukraine, he keeps promising more gas to Europe but not delivering, while Kremlin spokespeople explain the shortage could be alleviated when Germany finally certifies Nord Stream 2, a process that hit delays earlier this month.