While a lack of weapons, ammunition and equipment hampers the Ukrainian military, there are signs that a nascent partisan insurgency is growing in potency, allowing Ukrainian forces to deliver deadly strikes on Russian-controlled territory even in areas where it is dangerous and sometimes impossible to commit troops.
This week, partisan scouts working for Ukraine’s military behind enemy lines directed artillery attacks on two Russian bases in the occupied Kherson region that killed scores of enemy soldiers, according to a senior Ukrainian military official with knowledge of the attacks.
In one episode this week, the scouts approached a Russian army installation in the village of Chkalove, and discovered many foreign fighters stationed at the base along with Russian soldiers and heavy weaponry, the senior official said. They fed the coordinates for the base to a Ukrainian artillery unit stationed about 12 miles away.
The Ukrainians then pulverized the base with shells, killing scores of fighters just after midnight on Thursday, said the senior official, who spoke on the condition of anonymity to discuss sensitive military operations.
Oleksiy Arestovych, an adviser to President Volodymyr Zelensky of Ukraine, confirmed the attack and said about 200 fighters had been killed.
Later that day, scouts directed another artillery attack, this time on a resort complex in Stara Zburivka, near the mouth of the Dnipro River, killing dozens of enemy soldiers, including two generals, the senior official said. One of the generals was from the Russian army and another from Russia’s counterintelligence service, the F.S.B., the senior military official said.
The scouts are local partisans who aid the Ukrainian military on Russian-occupied territory. They might be former soldiers or simply civilians gathering information like the location of enemy units. They can be men pushing potato carts, or farmers, or a grandmother with a cellphone.
Ukrainian partisans have claimed credit for attacking Russian trains; targeting Russian proxies appointed to local government administrations; killing Russian soldiers; and supporting Ukrainian military efforts. Their support can prove crucial, both in southern Ukraine where Russia has captured territory, and in the east where Ukraine finds itself outgunned and fighting to hold onto its land.
Details of the two attacks this week could not be independently verified. The Russian foreign ministry did not respond to a request for comment.
The strike in Chkalove occurred near an area of active fighting in Ukraine’s south. To determine the number of dead, spotters counted body bags as they were loaded onto rescue vehicles, the senior official said.
The death toll in the strike was apparently so high because the shells struck a cache of munitions, sparking an explosion and a blaze that burned for six hours early Thursday morning, the official said.
The official said that before the attack, the partisans approached some of the foreign fighters and after trying to speak with them, surmised that they were Arab. The foreign fighters appeared to be living in tents near buildings occupied by Russian troops, the official said. He said they were possibly part of a contingent of Syrian troops that arrived in Russia three weeks ago.
It has long been rumored that Syrian fighters would join Russia’s fight in Ukraine, but there has been no official confirmation of this.
Mr. Arestovych, the adviser to Mr. Zelensky, said it was the first concrete evidence of the presence of Arab fighters in Ukraine.
The exact shape and size of the insurgency in southern Ukraine is unclear and the resistance to Russian occupation can come in many forms — from helping direct attacks on enemy forces in coordination with the Ukrainian military to posting leaflets on street corners to demoralize the occupiers. The goal always, according to scholars of insurgency, is to make sure the enemy never feels safe.
On June 3, the Ukrainian military command in southern Ukraine reported, without providing any evidence, that Russians were changing behaviors out of fear of the growing resistance.
“The leadership of the occupation authorities move around with large numbers of guards, in bulletproof vests, in armored cars,” the military command reported. “There is fear for their lives.”
During the first months of the occupation, witnesses described how Russian forces tried to locate anyone with a military or security background in the region to interrogate them. Amid continuing attacks by insurgents, witnesses have described increasingly draconian efforts to find possible rebels.
All traffic in and out of Kherson to Ukrainian-controlled land is now closed, and those who do move around can face a maze of checkpoints, with occupation forces checking cellphones for hints of pro-Ukrainian sympathies.
Russia-Ukraine War: Key Developments
The partisan resistance began in the first days of the war, when civilians armed with Molotov cocktails joined in attacks on invading Russian columns. But as Russia’s hold on the south deepened, it has had to become more clandestine.
Ukrainian news media have reported that the underground resistance in occupied territories is coordinated by a unit of its armed forces called the Special Operations Forces. The division was formed after attempts to build an insurgency to counter the Russian-backed separatists in the eastern Donbas region failed in 2015.
The Ukrainian government has set up a virtual Center of National Resistance that provides instructions for things like setting up ambushes and how to handle being arrested.
“In order to become an invisible avenger whom the occupiers will fear, it is necessary to know tactics, medicine, internet security, homemade weapons, and nonviolent actions,” the center’s website says.
In one example of the tips the government is giving to the resistance, it recently published an online step-by-step guide to hot-wiring Soviet-era armor.
Several attacks on Russian-appointed officials in the Kherson and Zhaporizhzhia regions have been reported by both Ukrainian and Russian officials — although the attacks are portrayed in vastly different ways. The Ukrainians praise the resistance. The Russians call the attacks acts of terror.
Andrei Shevchik, the pro-Kremlin mayor of Enerhodar — who was installed shortly after Russian forces occupied the Ukrainian city on the Dnipro River — was outside his mother’s home when he was seriously wounded in a blast. That appeared to be the work of insurgents, Russia’s RIA Novosti news agency reported on May 22, citing an emergency services worker in the city as a source.
Last week, an explosion struck close to the office of Yevgeny Balitsky, a pro-Kremlin Ukrainian official in the Russian-occupied city of Melitopol. Pro-Kremlin authorities in the city explicitly blamed Ukrainian partisans, and Russia’s Investigative Committee — the equivalent of the F.B.I. — blamed it on “Ukrainian saboteurs.”
Mr. Arestovych, the adviser to Mr. Zelensky, said there was a long tradition of waging guerrilla warfare in southern Ukraine, where the vast steppes leave the enemy little room to hide.
“Partisans are fighting very actively,” he said last month on his YouTube channel. “Both the Russian troops and the occupation administration are well aware of this.”