MOSCOW (AP) — Russian President Vladimir Putin on Tuesday made an unscheduled trip to Chechnya, a mainly Muslim republic within the Russian Federation, his first visit in nearly 13 years, as Ukraine's stunning cross-border incursion into western Russia entered its third week.

Putin was greeted by Chechnya’s self-styled strongman leader Ramzan Kadyrov, before visiting a special forces academy bearing his own name and speaking with volunteer fighters who train there prior to being deployed in Ukraine.

Putin praised the volunteers and said that as long as Russia has men like them, it will be “invincible,” according to reports by Russian state agencies.

Kadyrov said in a post on his official Telegram channels that more than 47,000 fighters, including volunteers, have trained at the facility since Moscow began what it calls its “special military operation” in Ukraine.

Fighters from Chechnya, whose bid for independence after the Soviet Union's collapse led to years of war with Russian government forces, are participating on both sides of the conflict in Ukraine.

Pro-Kyiv volunteers loyal to Dzhokhar Dudayev, the late Chechen pro-independence leader, are the sworn enemies of Chechen forces that back Putin and Kadyrov. The latter joined Russia in the months-long siege of Ukraine’s key port of Mariupol and other flashpoints in the country's south and east.

Also on Tuesday, Putin visited the grave of Kadyrov’s father, former Chechen leader Akhmat Kadyrov, a command post and a mosque in the local capital, Grozny.

At the end of the day, he held talks with the Chechen leader, who announced the republic has “tens of thousands" of reservists ready to fight the Ukrainians, according to Russian state media reports. The reports did not specify whether any of these might be sent to repel Kyiv's incursion into the Russian region of Kursk.

The Kremlin has relied on Kadyrov to keep the North Caucasus stable following years of turmoil. International rights groups have accused Kadyrov's security forces of extrajudicial killings, torture and abductions of dissenters, but Russian authorities have stonewalled repeated demands for investigations.

The Kremlin scrambled fighters from Chechnya to help protect Moscow from an abortive mutiny launched by mercenary chief Yevgeny Prigozhin last year, but some commentators warned that Kadyrov’s ambitions could also potentially pose a threat to federal authorities.

As of Tuesday evening, neither the Kremlin nor Kadyrov shared any details about the purpose and timing of Putin’s unexpected visit, with Kadyrov saying only that “a busy schedule” awaited the Russian leader.

Putin later held talks with Kadyrov at the Chechen leader's residence in Grozny.

Before his surprise visit to Chechnya, Putin was earlier on Tuesday in Beslan, a town in the Caucasus province of North Ossetia, where he had his first meeting in nearly two decades with mothers of children killed in the 2004 school attack by Islamic militants that left more than 330 dead.

At the meeting, he slammed Kyiv’s incursion into Russia's Kursk region, accusing the Ukrainians of “trying to destabilize” the country.

“We will punish the criminals. There can be no doubt about that,” he said.