KYIV — Windows trembled in Ukraine’s capital as Russia launched one of the largest attacks on the country since the start of the war. Air raid alarms erupted at six in the morning, warning citizens to run to the nearest shelter. Shortly after, the first explosions were heard.

Like everyone else, I bolted for the shelter. The streets at Kyiv’s main district, normally filled with pedestrians rushing to get to work, were now empty, as most civilians were sheltering in the nearest metro station. The few people who were wandering the streets ran for cover after a Russian ballistic missile — known for its loud explosions — fell on the outskirts of Kyiv and shook the city at nine in the morning. 

President Zelensky said about 15 Ukrainian regions have been targeted by one of the “biggest combined strikes” since the start of the war, as Russia launched more than 100 missiles and about 100 drones at Ukraine Monday. Following the attack, Mr. Zelensky urged Ukraine’s allies to lift restrictions on its weapons, including the ability to shoot down Russian missiles and drones in the neighboring territory. 

“Ukraine cannot be constrained in its long-range capabilities when the terrorists face no such limitations,” Mr. Zelensky said. “America, Britain, France, and our other partners have the power to help us stop this terror. The time for decisive action is now.”

The air raid alarm was active all morning across the country. People held their children tight to their chests in the shelter to prevent them from hearing the explosions. Footage posted on social media showed civilians in shelters singing Kyiv’s national anthem as they waited for the explosions to end. 

At least six people were killed in Ukraine’s Zaporizhzhia, Lutsk, Kharkiv, Zhytomyr, and Dnipropetrovsk, according to officials. Dozens were injured. Russians targeted the country’s energy infrastructure, triggering blackouts and water shortages in several regions. Ukraine’s largest private energy producer, DTEK, announced Monday it was introducing emergency power outages.

Russia said Monday that it had struck key energy infrastructure that supported Ukraine’s military-industrial complex. A Ukrainian deputy foreign minister, Andrii Sybiha, said Russia had targeted a hydropower plant in the Kyiv region. 

“These cowardly attacks are #warcrimes. Global action required: needs a right to long-range strikes & enhanced air defense,” Mr. Sybiha said. 

At the same time, Ukraine fears a threat from neighboring Belarus, which is concentrating a “significant number of personnel,” including mercenaries from the former Wagner private military company, on its border with Kyiv, close to Chernobyl’s nuclear power plant, Ukraine’s Ministry of Foreign Affairs said. 

According to officials, Belarus has also deployed weapons and military equipment, such as tanks, artillery, and anti-aircraft missiles. 

“Conducting exercises in the border zone and near the nuclear power plant, the Chernobyl NPP, poses threats to Ukraine’s national security and world security in general,” the statement said.  

Ukraine urged Belarus not to make “tragic mistakes” under Russia’s pressure. “In the event of a violation of Ukraine’s state border,” the statement says, Kyiv will take the necessary self-defense measures allowed by international standards. “All troop concentrations, military facilities, and supply routes on the territory of Belarus will be legal targets for the Armed Forces of Ukraine,” the statement adds. 

Monday’s events have led several Ukrainian officials to join President Zelensky’s plea to Western allies to lift restrictions. The main hashtag on social media platform X in Ukraine became #LetUkraineStrikeBack.

Ukraine’s Foreign Minister, Dmytro Kuleba, said Monday that Russia’s attacks must be “strongly condemned” by the international community. Mr. Kuleba said that partners should allow long-range strikes on “all legitimate military targets on Russian territory” and agree to the use of “air defense capabilities to shoot down missiles and drones close to their airspace.”

During Monday’s attack, warplanes of Ukraine’s neighbor, Poland, and its NATO allies were put on alert as Russia struck Ukraine’s western regions. Polish officials announced they had likely detected a drone in Polish airspace Monday that may have landed on their territory. 

“The object was confirmed by radiolocation by at least three radar stations. I had full control of the object, I was ready to shoot it down,” operational commander of Poland’s Armed Forces, General Maciek Klisz, said, according to the local press. A spokesman for the Polish army’s operational command told Reuters that searches were underway.