Russia's turn to mercenaries and foreign fighters hints at a much more brutal fight to come in Ukraine

• Russian forces invading Ukraine have struggled to overcome their logistical challenges and stiff Ukrainian resistance.
• Moscow now faces the prospect of hard fighting against determined defenders in major Ukrainian cities.

More than three weeks after Russia's invasion of Ukraine, President Vladimir Putin and his senior advisors understand that things aren't going as planned.

What was intended to be a quick "in-and-out" campaign to capture Kyiv and other cities and topple the Ukrainian government has become a protracted, bloody conflict that may be the worst Russian military disaster in decades.

A military adage is that no plan, however polished, survives first contact with the enemy. In war, the opponent gets a vote too, and even the best plans need to be flexible.

"I think by now everyone has seen that the war isn't going well for the Russians. They planned for a short campaign and a few days of operations but now they are facing a conventional war they weren't prepared for, and there is worse to come," a retired Green Beret told Insider.

Russia appears to have had poor intelligence about Ukrainian military capabilities and underestimated Ukraine's willingness to fight. The Russian advance has slowed to a crawl, and Moscow is now using heavy firepower to bombard Ukrainian cities.

The retired Green Beret, who has extensive experience in Europe but was not authorized to speak to the media, told Insider that the US Army's 10th Special Forces Group has trained Ukrainian troops well and that they're "prepared for a guerrilla phase."

"So even if the Russians succeed in the conventional phase of the war, they have hell waiting for them. I don't think the Russian population is ready for that. Even an authoritarian regime like Putin's can't weather thousands of body bags," the retired Green Beret added.

With casualties and costs mounting, and with hard fighting in Ukrainian cities ahead of them, the Kremlin is turning to other sources of manpower: Chechen fighters, private military contractors from the infamous Wagner Group, and Syrian mercenaries.

Mercenaries and foreign fighters

The Russian battle plan focused on speed, violence, and surprise, using a combination of special-operations forces, airborne troops, long-range fires, and multiple armored fronts across Ukraine to disorient and paralyze the Ukrainian military.

Chechen fighters and Wagner Group mercenaries appear to have been an integral part of that plan, with Moscow using them as shock troops to decapitate Ukraine's leadership at the outset of the war.

Ramzan Kadyrov, a Putin acolyte and head of Russia's Chechen Republic, said two days after the invasion that Chechen forces were in Ukraine and were ready to carry out Putin's orders "under any circumstances." Russia is already promoting stereotypes of Chechen brutality in its propaganda.

The Wagner Group is bankrolled by Yevgeny Prigozhin, a close Putin associate, and often pursues Russian foreign-policy goals despite its nominal independence. It has earned notoriety for its often brutal actions in Crimea, eastern Ukraine, Syria, Libya, and central Africa.

Reports indicate that Ukrainian President Volodymyr Zelenskyy has survived several assassination attempts by Chechens and Wagner mercenaries. Had they killed Zelenskyy and his Cabinet in the critical opening stage of the war, Ukraine's military might have conceded defeat.

Russian Defense Minister Sergei Shoigu has said more than 16,000 Arab volunteers are lining up to fight for Russia in Ukraine, and Russia's Ministry of Defense has released footage of Syrian mercenaries ready to deploy to Ukraine to support the invasion.

The Kremlin has reportedly managed to recruit roughly 3,000 Syrian fighters thus far, and the top US military official in the Middle East said Tuesday that only "very small" groups of people from that region are trying to make their way there. A senior defense official said Wednesday that the US had not seen indications that foreign fighters are in Ukraine right now.

Russia has justified the deployment of pro-Assad Syrian mercenaries as a response to the foreign fighters that are flocking from around the world to fight on Ukraine's behalf.

As Moscow shifts to combat in major Ukrainian cities, the foreign troops it brings in could put years of urban-warfare experience to use, though experts say they may struggle in the unfamiliar environment.

Foreign mercenaries are cheap and come with little political risk for Moscow, the retired Green Beret said. "No Russian will care if young Syrians die in Ukraine fighting for Putin. I suspect some will even be happy to learn that Chechens are dying there and see it as a 'win-win' situation."

But the retired operator said those foreign fighters may not fare better than the Russians have in Ukraine: "It's one thing to fight in the warm climate of Syria and another in the freezing Ukraine with mud so thick that it can literally stop a column of the most modern tanks."

Chechen and Syrian fighters are easy to find, don't cost much, and don't require the same amount of resources as regular troops, a former Navy SEAL officer told Insider, calling Russia's turn to them and other mercenaries "a sign of desperation."

The former SEAL, granted anonymity because they were not authorized to speak to the media, also pointed to a political motive.

"Putin will have to account for the deaths of Russian soldiers. We have seen from reports that not all Russians in Ukraine are professional soldiers. Large numbers of conscripts have been captured too (and more presumably killed). That is contrary to what Putin has said on Russian national television," a former officer said.

Stavros Atlamazoglou is a defense journalist specializing in special operations, a Hellenic Army veteran (national service with the 575th Marine Battalion and Army HQ), and a Johns Hopkins University graduate.