By Mike Collett-White and Stefaniia Bern
KYIV -At a memorial service on Tuesday for four Ukrainians killed last year while carrying out a raid on Russian territory, ordinary soldiers rubbed shoulders with volunteer fighters of the Brotherhood Battalion to which those killed belonged.
The ceremony, at the historic gold-domed St. Michael's cathedral in central Kyiv, underlined the unclear relationship between irregular groups and Ukraine's formal armed forces fighting against Russia.
The groups' role in the war is the focus of increasing scrutiny, after several videos purporting to show cross-border sabotage raids into Russian territory have surfaced and the Kremlin has raised the alarm over the security threat.
Reuters has not independently verified the videos.
Russian President Vladimir Putin has branded the saboteurs as "terrorists" and urged his security services to bolster defences along the frontier.
The four members of the Brotherhood Battalion later buried in Kyiv were Yurii Horovets, 34, Taras Karpiuk, 38, Maksym Mykhailov, 32 and Bohdan Liagov, 19.
They were killed on Dec. 25 last year, according to Russia's FSB security service, which said at the time that they were armed with foreign-made guns and four improvised explosive devices.
Ukrainian authorities did not comment on the raid then, and have subsequently denied involvement in attacks claimed by Ukrainian-based groups on Russian soil.
Last week, for example, a different group called the Russian Volunteer Corps led by a Russian nationalist in exile who opposes Putin's rule, said it had briefly taken control of a small border village.
Putin denounced that attack in a televised address, saying: "We will crush them". Ukraine portrayed it as a false "provocation" by Russia to justify its full-scale invasion.
Later the same day four members of Russia's National Guard were wounded when their car ran over a mine in the village of Sushany, just across the border from Ukraine, said Alexander Khinstein, a senior federal parliamentarian.
The raids present Kyiv with a dilemma. If regular forces were involved, it would represent a significant escalation in a war that has so far been fought almost exclusively on Ukrainian soil.
But Ukrainian officials have also cast the attacks, which have so far involved small armed groups on limited missions, as a sign Russians may take up arms against their leaders.
"Maybe Russians will begin to wake up," Ukrainian military intelligence spokesman Andriy Yusov said in response to the operation claimed by the Russian Volunteer Corps.
Ukraine is believed to have struck deep inside Russia on several occasions using drones, though officials decline to confirm them.
'PAIN AND PRIDE'
At the memorial for the Brotherhood fighters, whose bodies local media said were returned to Ukraine in late February, hundreds of soldiers and civilians crammed into the cathedral's ornate interior to watch priests bless the coffins.
Mourners lit candles and a man sobbed over one of the caskets.
Outside, as the coffins were being carried into the cathedral, the leader of the nationalist Brotherhood movement which is associated with the Battalion said he felt both "pain and pride".
"They were one of the most courageous ones to die in battle," Dmytro Korchynsky, a controversial figure in Ukraine for his ultra-nationalist and devout Orthodox Christian views, told Reuters.
"Our aim is to bring the war over to Russian territory. It's bad that the war is currently only on our territory, it has to expand to the enemy's territory as well."
Korchynsky was careful to distinguish between the battalion's activities in Ukraine, including areas occupied by Russians - where he said its members coordinate with Ukraine's armed forces - and those on Russian soil.
"When we are on Russian territory, we act autonomously," he added.
Ukraine's defence ministry did not immediately respond to a request for comment on its relationship with the Brotherhood Battalion, called "Bratstvo" in Ukrainian, and the armed forces.
The conservative nationalist Brotherhood movement began around 20 years ago to promote Christian values. Western media reports say it has been active in sometimes dangerous combat missions since Russia launched its full-scale invasion of Ukraine in February 2022.
Korchynsky said most of the Brotherhood volunteers were Christians, and that the numbers were "constantly growing.
"The battalion has several hundred fighters," he said. "We can't disclose precise numbers, as the battalion takes part in investigative and reconnaissance activity."
(Reporting by Mike Collett-White and Stefaniia Bern; Editing by Alex Richardson)