Executive Summary
- Monitoring Moscow’s oil revenues: Ukrainian long-range strike units continued to target Russian energy infrastructure. The Kremlin’s hydrocarbon revenues have suffered as a result.
- Russia’s new subterranean tactics: In the strategically important Kupiansk sector, Russia attempted to move troops through gas pipelines across the Oskil River.
- Potential Cuban involvement: American and Ukrainian officials drew attention to the growing number of Cuban mercenaries fighting for Russia.
1. Battlefield Assessment
Over the last week, the Russian military has conducted a hybrid assault near Kupiansk, combining subterranean warfare with an intensive river-crossing operation.
The assault on Kupiansk is central to the Kremlin’s efforts in the Kharkiv sector. To that end, Moscow attempted to move its forces closer to the city by sneaking troops through gas pipelines across the Oskil River. Ukrainian forces placed razor wire in some pipelines and flooded others to help repel the hybrid attack, with mixed results. This report will track the situation near Kupiansk as Russia’s subterranean campaign unfolds.
Ukraine continued to launch strikes deep inside Russia to disrupt the Kremlin’s hydrocarbon revenues and damage Russian military stockpiles. Recent reports indicate that Ukrainian salvos have meaningfully diminished Russia’s energy exports and refining capacity. Over the last two months, Kyiv targeted almost half of Russia’s major refineries, with drones inflicting the most damage. Ukrainian Main Directorate of Intelligence (GUR) units also continued to hit Russian military targets behind the front lines, particularly in the occupied Crimean Peninsula.
Nonetheless, the strategic situation continues to favor the invaders. In the summer of 2025, Russia’s military gained more than twice the territory it captured during the equivalent period in 2024. While Ukrainian forces have inflicted heavy casualties, Russia has made steady gains throughout the year.
In the wider battlespace, fighting raged at a pressing operational tempo across the usual flashpoints, including Pokrovsk, Toretsk, Lyman, Siversk, Vovchansk, and Orikhiv. Pokrovsk, once again, witnessed the most intense combat.
2. Cuban Mercenaries Fight in Ukraine
On September 18, Ukrainian and American officials participated in a virtual briefing sponsored by Representative Mario Díaz-Balart (R-FL). The briefing aimed to raise awareness of the “alarming presence” of Cuban regime troops fighting for Russia in Ukraine.
The discussion featured members of the Florida state legislature, Cuban opposition figures, and Ukrainian officials including Vladyslav Vlasyuk, an advisor to President Volodymyr Zelenskyy; Andriy Yusov, a spokesman for the GUR; and Oleksandr Merezhko and Maryan Zablotskyy, members of Ukraine’s parliament.
In his briefing, Yusov revealed that as many as 20,000 Cubans may be fighting for Russia. The GUR has confirmed that 39 Cubans in Russia’s ranks have already been killed in action and that thousands more have signed contracts to fight for the Kremlin. Many of the Cubans captured by the Ukrainian military attest that they were lured into the war under the false pretense that they would join noncombat logistics brigades behind the front lines. Yusov also stated in the briefing that “such recruitment could not have taken place without the blessing of the Cuban regime.”
Defense analysts have uncovered additional evidence of Cuban involvement in the Russian invasion. Records leaked by Ukrainian hackers in September 2023 allege that the Russian military had attempted to recruit nearly 200 Cuban mercenaries. Previous open-source intelligence assessments have determined that elements from Cuba’s elite special forces, known as the Avispas Negras or “Black Wasps,” have fought in Ukraine since around that same time. These units have likely acted as liaisons to lay the foundations for a larger group of combat-ready Cuban fighters.
Russian units have already incorporated large numbers of North Korean fighters. It appears the Kremlin may have augmented its forces with another sizable contingent of foreign troops.