Strikes across Ukraine, Russian-occupied territory and Russia killed at least 16 people, authorities said, as the 40th anniversary of the Chernobyl nuclear disaster prompted fresh warnings about the risks posed by attacks near the plant during Russia's more than four-year invasion of its neighbor.

The death toll from Russian drone and missile strikes on the city of Dnipro rose to nine, regional head Oleksandr Hanzha said Sunday.

One man was killed in a Ukrainian drone strike on the port city of Sevastopol, in Russian-occupied Crimea, Moscow-installed authorities said Sunday. Russia annexed the peninsula from Ukraine in 2014, a move that most of the world considered illegal, and has used it as a staging and supply point during the war.

Leonid Pasechnik, the Russia-installed governor in Ukraine's Luhansk region — of which Russia earlier this month said it had taken full control, a claim denied by Ukraine — said three people were killed in an overnight Ukrainian drone strike on a village, after reporting two people were killed in the early hours of Saturday.

Ukraine did not comment on either attack, which could not be independently verified by The Associated Press.

The latest strikes came after a woman was killed in a Ukrainian drone attack on Russia's Belgorod border region, according to local authorities.

Ukrainian forces also struck an oil refinery in Yaroslavl, deep inside Russian territory, Ukraine's General Staff said Sunday. The strikes sparked fires at the facility, which processes 15 million tons of oil a year and produces gasoline, diesel and jet fuel for the Russian military. Russia did not immediately comment.

Ukraine has developed its own long-range drones, which can reach targets some 1,500 kilometers (900 miles) inside Russia. It has used them recently against Russian oil facilities as Moscow looks to boost its exports after the Trump administration gave it a temporary waiver from sanctions to ease supply constraints. Kyiv officials complain that Russia will use the additional revenue on new weapons to hit Ukraine harder.

Ukraine's President Volodymyr Zelenskyy marked the anniversary of the Chernobyl nuclear disaster to warn that Russian attacks risk repeating history.

"Through its war, Russia is once again bringing the world to the brink of a man-made disaster — Russian-Iranian Shaheds regularly fly over the plant, and one of them struck the confinement last year," he wrote on Facebook.

"The world must not allow this nuclear terrorism to continue, and the best way is to force Russia to stop its reckless attacks," he said.

Rafael Grossi, director general of the International Atomic Energy Agency, echoed those concerns during a visit to Kyiv, saying repairs to the plant's damaged outer protective shell must begin immediately. IAEA assessments show the damage sustained after a strike last year has already compromised a key safety function of the structure, he said, warning that years of inaction could heighten danger to the original sarcophagus beneath it. The European Bank for Reconstruction and Development said repairs would require at least 500 million euros ($586 million).

Ukrainian officials say a Russian drone struck the outer shell of the plant's New Safe Confinement structure — a $2.1 billion archlike enclosure completed in 2019 over the remains of Reactor No. 4 — in February 2025. Moscow denied targeting the plant, alleging Kyiv staged the attack.

Russia's Defense Minister Andrei Belousov visited North Korea on Sunday for talks with North Korean leader Kim Jong Un about future military cooperation between the countries.

Belousov said the countries agreed to "transition military cooperation to a sustainable, long-term basis," according to Russia state news agency Ria Novosti.

During the visit, he presented the Russian Order of Courage to Korean service members who served in Russia's Kursk region, where Ukraine launched a surprise incursion in August 2024.

Kim has sent thousands of troops and large weapons shipments to support Russia's war against Ukraine.