MICHEL MARTIN, HOST:

This weekend, Russia faced another setback to its military campaign in Ukraine - a massive explosion at a key bridge linking the Russian mainland to the illegally annexed peninsula of Crimea. Russia reports that at least three people died in that blast. And shortly after, Russian President Vladimir Putin announced that a new commander would be taking over the war effort. And today, he called the explosion a terrorist attack. To talk more about these developments and what they could mean for the war, we called NPR's Charles Maynes in Moscow. Charles, thanks so much for joining us.

CHARLES MAYNES, BYLINE: Happy to join you.

MARTIN: So could you just, first of all, bring us up to speed? How did this explosion on the bridge happen, and what's been the reaction?

MAYNES: Well, the Russian authorities' working theory has been that it was a truck bomb. Surveillance video shows a massive fireball erupting as a truck was traveling across this 12-mile Kerch Strait Bridge on Saturday morning. Whatever the cause, two sections of road collapsed into the water, a portion of the railway line was badly damaged after tankers carrying fuel also caught fire - this created these dramatic images of a fireball along the bridge.

Now, today, President Putin ended a period of initial silence to outright label the incident a terrorist attack carried out by Ukraine's security services. What response from Russia is forthcoming? We don't yet know. There's certainly plenty of nationalists here who say this "attack," in quotation marks, cannot go unanswered, and they're demanding a massive show of force. Just today, we also saw Russia carry out a barrage of airstrikes on the southern Ukrainian town of Zaporizhzhia, killing at least a dozen people. Whether that's somehow linked to the bridge incident, though, we simply don't know.

MARTIN: So, Charles, this war - this conflict has been going on for seven months now, and we see the destruction has been everywhere. So what makes this bridge - this particular incident - so critical?

MAYNES: Well, it's a symbol of Russia's hold over Crimea in the wake of its illegal annexation of the peninsula in 2014 - you know, kind of an umbilical cord to show that Crimea and Russia's mainland are one entity. And it was Putin's personal triumph. You know, his government built what the czars and Soviets couldn't, and to underscore that point, it was Putin who opened the bridge. Somewhat ironically, he drove a truck across the bridge when it first opened in 2018. Now, Ukraine has been coy about any role in the blast but made no secret this bridge would be a desirable military target. And that's also because, beyond its symbolic value, the bridge has a very real implication for the Russian military campaign. It's the key supply line for Russian troops operating in the south of Ukraine, and damage to it comes at a time when the Russian military has really struggled there.

MARTIN: So speaking of that, Russia announced that there's a new commander for its Ukraine operations. Do we know who he is and what this change may signify?

MAYNES: Yeah, sure. His name is General Sergey Surovikin, and it's rather unusual that Moscow made this news public. Surovikin was already leading Russia's southern forces in Ukraine and really got that job based on a reputation for success and brutality in Syria, where Russia has intervened on behalf of its ally, Bashar al-Assad, over the last five years. What's important here - the announcement comes at a moment when some influential Kremlin allies are openly accusing Russia's defense ministry of incompetency over these recent territorial losses. And these critics, you know, they've welcomed Surovikin's promotion.

MARTIN: That's NPR's Charles Maynes in Moscow. Charles, thanks so much.

MAYNES: Thank you. Transcript provided by NPR, Copyright NPR.