Fires and ammunition exploded at a warehouse in Crimea on Wednesday, a day after the latest suspected Ukrainian attack on a military site on the Russian-annexed peninsula, underscoring the challenges facing Moscow. The peninsula, which Russia captured in 2014, was once a safe base used by Moscow’s forces to launch attacks — and was a staging ground for the launch of the February 24 invasion. But in recent days, explosions have destroyed several Russian planes at an air base in Crimea, and munitions exploded on Tuesday. Ukrainian authorities have not publicly claimed responsibility, but President Volodymyr Zelenskyy referred to Ukrainian attacks behind enemy lines after the latest explosions on Tuesday, while Russia blamed “sabotage”. The spate of attacks represented the latest setback for Moscow, which launched its invasion with hopes of taking the capital Kiev and much of the country in a flash, but soon bogged down in the face of tougher-than-expected resistance from Ukrainian forces. As the war nears its end of the semester, the sides are now in a war of attrition, fighting village by village, largely in the east of the country. Attacks in Crimea could open a new front that would represent a major escalation of the war and further expand Russia’s military resources. “Russian commanders are likely to be increasingly concerned about the apparent deterioration in security across Crimea, which acts as a rear base area for the occupation,” Britain’s Ministry of Defense tweeted. But it was unclear whether the Crimea attacks would break the stalemate as Ukrainian and Russian forces clash in a war that has driven millions from their homes, disrupted food supplies around the world and occasionally sparked fears of a nuclear accident . On Thursday, UN Secretary-General Antonio Guterres plans to travel to Ukraine to meet with Zelensky and Turkish President Recep Tayyip Erdogan to discuss removing grain shipments critical to feeding the world’s hungry. They are also expected to talk about a possible fact-finding mission to the Russian-controlled Zaporizhzhia nuclear power plant, which Moscow and Kyiv have accused each other of bombing. Tuesday’s explosions and fires broke out at an ammunition depot near Dzhankoi in Crimea, leading to chaotic scenes when about 3,000 people had to be evacuated. In a vivid reminder of Russia’s vulnerability in Crimea, the peninsula’s regional leader, Sergei Aksionov, said authorities were still battling the fires Wednesday with a helicopter as the mines continued to erupt. He said investigations to identify the perpetrators of the attack are ongoing. Business newspaper Kommersant also reported explosions on Tuesday at a base in Gvardeyskoye. As of Wednesday, there was still no comment from Russian authorities. The British intelligence report noted that Gvardeyskoye and Dzhankoi “host two of the most important Russian military airfields in Crimea.” A week earlier, the Russian military came under pressure on the peninsula when Ukraine said nine Russian warplanes were destroyed after explosions at the Saki air base in Crimea. The huge explosions sent plumes of smoke billowing over nearby beaches and sent sunbathers fleeing. At the time, Moscow hinted that the blasts were accidental, perhaps caused by a careless smoker, an explanation that drew derision from Ukrainian authorities who hinted at involvement in the attack but did not immediately claim responsibility. On the eastern front, the stalemate continued, with the bombing causing more and more death and destruction. In the Donetsk region that is the focus of the Russian offensive, two civilians have been killed and seven others injured in recent Russian shelling of several towns and villages. Meanwhile, in the south, Russian long-range bombers fired cruise missiles at the Odesa region overnight, injuring four people, regional administration spokesman Oleh Bratchuk said. In Mykolaiv, also in the south, two Russian rockets destroyed a university building early Wednesday, but no one was injured. Russian forces also shelled Kharkiv in the northeast and various parts of the surrounding area overnight, damaging residential buildings and civilian infrastructure, but causing no casualties.