Kharkiv, Ukraine — Major cities across Ukraine, including the capital Kyiv, were targeted yet again by Russian cruise missiles and drones in the early morning hours of Friday. Russia has upped the intensity of its aerial attacks in recent weeks, attempting to disrupt preparations for a long-anticipated Ukrainian counteroffensive.

One missile slammed into a clinic in the eastern city of Dnipro later Friday morning, killing at least one person and wounding 15 more, Ukrainian President Volodymyr Zelenskyy said on Twitter, calling it "another crime against humanity."

But there has also been an increase in attacks inside Russia. Dissident groups of Russian nationals opposed to President Vladimir Putin and his war in Ukraine have carried out attacks in border cities including Bryansk and Belgorod.

• Wagner boss, "Putin's butcher," warns Russia could face a new revolution

From a bomb blast in Moscow that killed a vocal advocate of the Ukraine invasion, to the most recent cross-border raids in Russia's Belgorod region there's been increasing evidence of armed resistance to Putin's war, inside Russia.

A collection of disparate anti-Kremlin armed groups are behind the attacks. They have divergent political views and ideologies, but they're united by a common goal:

"To ensure the collapse of the Russian regime as quickly as possible," in the words of a masked gunman from one of the groups, who spoke with CBS News for a rare on-the-record interview.

We sent written questions to one of the partisan groups that's claimed responsibility for some of the recent attacks on Russian soil. 

The fighters, heavily disguised, said they derailed a train in Bryansk earlier this month in their most successful action to date. They gave us video purportedly showing them setting off an explosion and throwing a Molotov cocktail at a Russian electrical substation. 

• Denmark and Netherlands to lead F-16 training for Ukrainians

"We are destroying military targets and support infrastructure," the masked spokesman of the armed group told CBS News.

CBS News cannot independently verify the group's claims, and audacious attacks this week on Russian towns in the Belgorod region, which borders Ukraine, were launched by two other partisan organizations calling themselves the Russian Volunteer Corp and the Free Russia Legion.

Fresh from those raids, they held a brazen news conference near the Russian border in eastern Ukraine, with Volunteer Corps commander Denis Kapustin, who's known for his ultra-right-wing leanings, threatening more attacks. 

"Phase one we consider a successful phase," he said. "It's over now but the operation is ongoing. That's all I can say for now."  

Kapustin said no American military equipment was used in the attack, and the masked men we spoke with said they could get any weapons they needed thanks to a huge black market that's arisen as a result of Putin's war.

The group has threatened more attacks.

Russia's state-run RIA Novosti news agency quoted officials Friday, meanwhile, as saying a Russian national had been arrested and accused of plotting an attack in the Black Sea resort town of Gelendzhik, not too far from Ukraine's Russian-occupied Crimean Peninsula.

There were no immediate claims of responsibility for the alleged plot, but RIA said officials had identified the suspect as "a supporter of Ukrainian neo-Nazism, a Russian citizen," who was plotting an attack against "law enforcement agencies in the region."

CBS News' Tucker Reals contributed to this report.

In:
• Wagner Group
• War
• Ukraine
• Russia
• Vladimir Putin
• Revolution
• Moscow