In the first days of his war on Ukraine, Russian President Vladimir Putin looked to Chechen warlord Ramzan Kadyrov to supply the fighters he wanted to take an airfield north of Kyiv and launch Russia’s advance on the capital.

       That unit was pummeled and its commander was killed by Ukrainian forces when it tried to seize the Hostomel Airport. But Mr. Putin has turned again and again to Mr. Kadyrov’s forces from Chechnya, reveling in the Chechens’ fearsome reputation as Russia steels for another push on the capital—and Mr. Kadyrov appears happy to comply.

       “We are in Hostomel, these days we are 20 kilometers away from you," Mr. Kadyrov said on his personal Telegram channel earlier this week, goading Ukrainians bracing for the onslaught in Kyiv. “Should I knock on your door?"

       A shaky video showed him in a darkened bunker, laughing with Chechen military officers looking over documents blurred out on screen, though Ukrainian sources say it wasn’t shot in Ukraine and said some server logs from Mr. Kadyrov’s web activity showed he was in Chechnya at the time.

       In many ways, the relationship between Mr. Putin, the Muslim Chechens and Mr. Kadyrov in particular, has become symbiotic. Mr. Putin burnished his reputation in the early years of his rule by sending troops into Chechnya, a Russian republic on the country’s southern flank, to put down an Islamist insurgency. Mr. Kadyrov’s father, Akhmat Kadyrov, a rebel religious leader, sensed which way the wind was blowing and pledged allegiance to the Kremlin, helping the Russian forces put down the separatist movement and routing the capital, Grozny.

       After his father was killed in a bomb attack, the younger Mr. Kadyrov strengthened his family’s alliance with Moscow. He ensured Chechnya’s loyalty in return for vast inflows of cash that enriched his family and helped him build a huge security apparatus that at times has served as his personal army. His forces have since been implicated in some of the worst rights abuses in modern Russia, including the mass detentions of Mr. Kadyrov’s opponents, along with allegations of torture and the disappearance of both his critics and ordinary citizens, say Russian and international human rights groups.

       “For Ramzan, this is to show Vladimir Putin that his loyalty knows no bounds and that he will send in his own men to support the president’s mission in Ukraine," said Alexey Malashenko, an expert on Russia’s North Caucasus at the Moscow-based Institute of World Economy and International Relations.

       By deploying his forces behind Mr. Putin’s war in Ukraine, Mr. Kadyrov is also making a public show of support that is designed to show any rivals in Chechnya that he is tightly aligned with the Russian state and to remind them of the firepower at his command.

       For Mr. Putin, having Chechen national guard battalions at his disposal provides a corps of troops who might be able to restore the sense of intimidation that Russian soldiers have largely lost since the start of the invasion, when fierce Ukrainian resistance cost the lives of several thousand Russian soldiers and the loss of numerous tanks and aircraft.

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       While their numbers are unclear, Moscow will likely use Mr. Kadyrov’s forces for any street-to-street fighting that would likely accompany any effort to take Kyiv.

       “They’re not trained for the conventional battlefield," said Munira Mustaffa, executive director of Chasseur Group and nonresident fellow at New Lines Institute for Strategy and Policy. “They’re there to hype up their image as fearsome warriors and sell their reputation for savagery that they earned in putting down the Chechen insurgency."

       Mr. Kadyrov’s forces have been deployed in other hot spots before.

       They were stationed in Crimea before Russia annexed the Ukrainian peninsula in 2014. In Syria they fought other Chechen fighters who had been fighting against Mr. Putin’s ally, President Bashar al-Assad, and they often led the line as the Syrian government retook a wave of towns and cities.

       Days before the deployment at Hostomel Airport, Mr. Kadyrov marched national guard troops outfitted with rocket-propelled grenades and machine guns through the streets of Grozny. In a flashy video posted on his personal Telegram page, Mr. Kadyrov, flanked by his sons and Chechnya’s official mufti, said 12,000 Chechens were ready to fight in Ukraine.

       “I gathered you, we should be ready for anything," he said.

       However, the independence of the Chechen units in Ukraine has caused problems in coordination with Russian troops. It could have been a factor in the battle for Hostomel Airport, where troops from the 41st motorized regiment of the Chechen national guard were killed along with their leader Magomed Tushayev. The Chechen battalions have largely remained self-sufficient without integrating into broader Russian military troop structures. They travel together and speak largely in Chechen on videos posted on Mr. Kadyrov’s social media pages.

       Other Chechen units have come into Ukraine from the east and are now on the outskirts of Mariupol, the besieged Ukrainian city on the Sea of Azov. Mr. Kadyrov’s close ally, Adam Delimkhanov, also a lawmaker in Moscow, is leading Chechen troops against Ukrainian forces that have taken a position at the Azovstal Iron and Steel Works.

       Ukrainian troops have taken to taunting the Chechens as well. Ukraine’s National Guard posted a video of fighters from the Azov Battalion, some members of which were accused of committing potential war crimes by the United Nations in 2016, greasing bullets in pork fat and warning them to go home.

       The invasion has also given a chance for anti-Kremlin Chechen groups to take aim at Mr. Kadyrov’s forces. One former native of Grozny, who has been living in Kyiv since fleeing Chechnya after the imposition of Russian rule, has joined a battalion of Chechens fighting for Ukraine.

       “I plan on fighting to show the world who Chechens are and how we’re different from Kadyrov’s thugs," he said.

       This story has been published from a wire agency feed without modifications to the text

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       Topics russia-ukraine crisis