A small explosive device carried by a makeshift drone blew up Sunday at the headquarters of Russia's Black Sea Fleet on the Crimean Peninsula, wounding six people and prompting the cancellation of ceremonies there honoring Russia's navy, authorities said.
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Meanwhile, one of Ukraine's richest men, a grain merchant, was killed in what Ukrainian authorities said was a carefully targeted Russian missile strike on his home.
There was no immediate claim of responsibility for the drone explosion in a courtyard at the naval headquarters in the city of Sevastopol. But the seemingly improvised, small-scale nature of the attack raised the possibility that it was the work of Ukrainian insurgents trying to drive out Russian forces.
A Russian lawmaker from Crimea, Olga Kovitidi, told Russian state news agency RIA-Novosti that the drone was launched from Sevastopol itself. She said the incident was being treated as a terrorist act, the news agency said.
Crimean authorities raised the terrorism threat level for the region to "yellow," the second-highest tier.
Sevastopol, which was seized along with the rest of Crimea from Ukraine by Russia in 2014, is about 170 kilometers (100 miles) south of the Ukrainian mainland. Russian forces control much of the mainland along the Black Sea.
The Black Sea Fleet's press service said the drone appeared to be homemade. It described the explosive device as "low-power." Sevastopol Mayor Mikhail Razvozhaev said six people were wounded. Observances of Russia's Navy Day holiday were canceled in the city.
Ukraine's navy and an adviser to President Volodymyr Zelenskyy said the reported drone attack underlined the weakness of Russian air defenses.
"Did the occupiers admit the helplessness of their air defense system? Or their helplessness in front of the Crimean partisans?" Oleksiy Arestovich said on Telegram.
If such an attack is possible by Ukraine, he said, "the destruction of the Crimean bridge in such situations no longer sounds unrealistic" – a reference to the span that Russia built to connect its mainland to Crimea after the annexation.
Elsewhere in Ukraine, the mayor of the major port city of Mykolaiv, Vitaliy Kim, said shelling killed one of Ukraine's wealthiest men, Oleksiy Vadatursky, and his wife, Raisa. Vadatursky headed a grain production and export business.
Another presidential adviser, Mykhailo Podolyak, said Vadatursky was specifically targeted.
It "was not an accident, but a well-thought-out and organized premeditated murder. Vadatursky was one of the largest farmers in the country, a key person in the region and a major employer. That the exact hit of a rocket was not just in a house, but in a specific wing, the bedroom, leaves no doubt about aiming and adjusting the strike," he said.
Vadatursky's agribusiness, Nibulon, includes a fleet of ships for sending grain abroad.
Meanwhile, Zelenskyy said that the war has significantly reduced the size of Ukraine's grain harvest compared with past years, but that Ukraine is working on ways to export what it has to avoid a global food crisis.
"The Ukrainian harvest this year is in danger of being half as large," he said on Twitter.
Russia and Ukraine recently reached an agreement that would allow the release of millions of tons of grain held up in Black Sea ports. Officials have said they expect the shipments to begin soon.
Ukraine war hangs over UN meeting on nukes treaty's legacy
There was already plenty of trouble to talk about when a major UN meeting on the landmark Nuclear Nonproliferation Treaty was originally supposed to happen in 2020.
Now, the pandemic-postponed conference is finally slated to start Monday as Russia's war in Ukraine has reanimated fears of nuclear confrontation and cranked up the urgency of trying to reinforce the 50-year-old treaty.
"It is a very, very difficult moment," said Beatrice Fihn, the executive director of the Nobel Peace Prize-winning International Campaign to Abolish Nuclear Weapons.

(AP via Martial Trezzini/Keystone | Archive)
Russia's invasion, accompanied by ominous references to its nuclear arsenal, "is so significant for the treaty and really going to put a lot of pressure on this," she said. "How governments react to the situation is going to shape future nuclear policy."
The four-week meeting aims to generate a consensus on the next steps, but expectations are low for a substantial – if any – agreement.
Still, Swiss President Ignazio Cassis, prime ministers Fumio Kishida of Japan and Frank Bainimarama of Fiji, and more than a dozen nations' foreign ministers are among attendees expected from at least 116 countries, according to a UN official who spoke on condition of anonymity because he wasn't authorized to speak publicly before the conference.
In force since 1970, the Nonproliferation Treaty has the widest adherence of any arms control agreement. Some 191 countries have joined.
When launching the Ukraine war in February, Russian President Vladimir Putin warned that any attempt to interfere would lead to "consequences you have never seen" and emphasized that his country is "one of the most potent nuclear powers." Days later, Putin ordered Russia's nuclear forces to be put on higher alert, a move that UN Secretary-General António Guterres called "bone-chilling."
"The prospect of nuclear conflict, once unthinkable, is now back within the realm of possibility," he said.
Ukraine is hardly the only hot topic.
North Korea appears to have been preparing recently for its first nuclear weapons test since 2017. Talks about reviving the deal meant to keep Iran from developing nukes are in limbo.
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The US and Russia have only one remaining treaty curtailing their nuclear weapons and have been developing new technologies. Britain last year raised a self-imposed cap on its stockpile. China says it's modernizing – or, the US claims, expanding – the world's third-largest nuclear arsenal.
Daryl Kimball, who heads the nonprofit Arms Control Association in Washington, can't recall another time when the Nonproliferation Treaty has come up for review with "so many difficulties in so many different areas, and where we have seen such severe tensions between the major players."
US Ambassador Adam Scheinman, the presidential special representative for nuclear nonproliferation, said Washington hopes for a "balanced" outcome that "sets realistic goals and advances our national and international security interests."
"You can have no doubt that Russia's actions will affect the climate at the conference and prospects for an agreed outcome document. Other difficult issues may complicate this, as well. But I'm prepared to be somewhat optimistic," he said in a telephone briefing.
In Beijing, Chinese Foreign Ministry spokesperson Zhao Lijian said his country wants to work toward improving global nuclear governance and upholding the international order and will "firmly safeguard the legitimate security and development interests and rights of China and the developing world."