Ukraine Hits Russian Positions Deep Behind Enemy Lines

KYIV, Ukraine — Ukraine found a way to hit deep behind enemy lines with a series of mysterious explosions in Russian-held territory early Wednesday, even as Ukrainians themselves were warned that Moscow appears poised to unleash a new barrage of attacks.

Half a year after the southern port city of Mariupol fell to a fierce Russian siege, nearly a dozen explosions were reported there overnight into Wednesday. Russian-occupied areas of the Donetsk, Luhansk and Kherson regions were also hit, according to reports and video.

What targets were struck was perhaps less intriguing than how Ukrainian forces had managed to hit them.

After taking control of Mariupol in the spring, Moscow gradually turned the city into a major garrison, apparently because it was thought to be out of the range of powerful U.S.-provided missiles in the nearest Ukrainian stronghold, near the ruined mining town of Vuhledar.

But at least 11 explosions were reported Wednesday by the exiled City Council. One of them destroyed a Russian ammunition warehouse in the district near the airport, the council said.

It was not the first time explosions have been reported deep behind enemy lines during the war, but questions swirled on Wednesday about what had happened. In the past, the Ukrainians have used drones, special operators working behind enemy lines and a vast network of partisans loyal to Kyiv to wage war on the occupiers.

The Ukrainian General Staff said only that Ukraine’s air force had launched eight attacks on the temporary bases of Russian troops and two strikes on the positions of Russia’s antiaircraft missile systems.

For Moscow’s part, the Russian-appointed local administrator in Mariupol claimed that everything was fine and said Russian air defenses had shot down two Ukrainian drones attacking the city overnight.

Explosions also sounded on Wednesday in Kharkiv, a Ukrainian city still under government control, as the authorities issued nationwide air alerts and warnings that Russia was planning a large-scale missile barrage timed to Friday’s anniversary of its invasion.

In Kharkiv, a half-dozen thunderous booms echoed through the city shortly before 11 a.m. It was not immediately clear what was hit. A few minutes later, an air alert was canceled.

There was no way to know whether the volley of missiles that hit the city was a prelude to a larger attack or simply more of the same. The city lies near the Russian border, and it is often struck by shorter-range missiles that cannot reach more distant cities such as Kyiv, the capital.

Taking no chances, the government has advised Ukrainian schools to operate remotely later this week.

The school system has already been upended because of the war. Schools struggled to operate during the major power outages caused by Russian strikes on critical infrastructure, and explosions have left many classrooms across Ukraine unusable. School officials said that Russian attacks have damaged 3,128 educational institutions, 441 of which are beyond repair.

Since October, Russia has launched volleys of missiles and exploding drones every week into Ukraine, mostly aimed at electrical plants, transmission lines and transformer substations. The goal is to knock out power and heat during the winter months, demoralizing the populace.

In recent days, with the start of the war’s anniversary nearing, the Ukrainians say they have detected stepped-up enemy activity, including frequent flights by Russian planes capable of launching missiles and balloons being floated over Ukraine, possibly as decoys to confuse air defenses.

In a war where civilian area have often been targeted, tensions tend to increase around anniversaries and holidays.

In August, as Ukraine celebrated its Independence Day, a Russian missile strike hit a rail station east of the city of Dnipro, crushing passenger cars and setting them afire. At least 22 civilians were killed and 50 were wounded. And on New Year’s Eve, strikes rained down on Kyiv, killing one person and partially destroying a hotel.

Now, with the Kremlin staging celebrations of the war in Moscow, some analysts have suggested that Russia might soon fire a larger than typical barrage not just to mark the anniversary of the Feb. 24 invasion but to try to overshadow the military setbacks it has suffered in a year of war.

A barrage might also serve as a pointed rejoinder to the West, coming just days after Ukraine’s allies pledged to maintain their military support and President Biden made a surprise visit to Kyiv.

Kyiv has also been casting an anxious eye on Russian threats via two neighboring countries, Belarus and Moldova.

Experts say they appear to pose minimal immediate risks, and military analysts have expressed doubt about Russia’s ability to open and sustain a new front in the war. But Western officials warn that Moscow could try and divert Ukrainian resources through feints and deceptions — which could come from anywhere.

Still, the main thrust of Moscow’s offensive operations remains in eastern and southern Ukraine, where Russian forces are trying to break through Ukrainian defenses in five directions.

“Despite all the pressure on our forces, the front line has not changed,” Mr. Zelensky said in a late-night address on Tuesday.

Marc Santora reported from Kyiv, Ukraine, and Andrew E. Kramer from Kharkiv, Ukraine. Carly Olson contributed reporting from New York.