As Russia tries to solidify its ‘land bridge,’ Ukraine attempts to push back in the south.

As Russia wages a destructive war in eastern Ukraine, its forces have been busy trying to restore transportation links and other key infrastructure in the vast stretch of land it occupies in the south.

Defense Minister Sergei K. Shoigu said on Tuesday that Russia’s military, working with Russian Railways, had repaired about 750 miles of track in southeastern Ukraine and set the conditions for “full-fledged traffic” to flow from Russia, through Ukraine’s eastern Donbas region, to occupied territory in Kherson and on to Crimea.

He also said that water was once again flowing to Crimea through the North Crimean Canal — an essential source of freshwater that Ukraine cut off in 2014 after the Kremlin annexed the peninsula.Satellite imagery reviewed by The Times showed that water was flowing through the parts of the canal in Crimea that were dry until March 2022.

Russia’s other claims could not be verified, and Ukrainian officials did not immediately comment. But the announcements showed that even as Moscow has redirected the bulk of its combat forces to the industrial eastern region known as Donbas, it is working to cement its hold over lands it has seized in the south.

Creating a “land bridge” from Russia to territory captured in southern Ukraine would accomplish one of Moscow’s major objectives in the war, analysts say.

Of the 20 percent of Ukraine’s territory now occupied by Russia, the largest swath of newly occupied land stretches across the southern regions of Kherson and Zaporizka. Occupying forces have introduced Russian currency and appointed proxy officials in both regions, but Moscow’s claim that it has restored infrastructure links offers an even clearer sign that the Kremlin intends to keep these lands for itself.

A key prize is the North Crimean Canal, which once provided some 85 percent of the freshwater used by people living on the Crimean Peninsula.

In 2014, after Russia annexed Crimea in a move that Ukraine and its Western allies called illegal, the Ukrainian government built a dam in the town of Kalanchak to block the canal’s flow south. Hours after President Vladimir V. Putin ordered Russian forces to invade Ukraine on Feb. 24, Russian forces seized the canal.

Petro Lakiychuk, an analyst at the Center for Global Studies “Strategy XXI” think tank in Kyiv, told Ukrainian state media that the canal was vital to the Kremlin’s long-term plans.

“The enemy will stay there with all its strength, sparing no people,” Mr. Lakiychuk said.

The restoration of the rail lines could also help Russia, allowing heavy weapons to flow into occupied Ukraine by rail and giving Russia a foothold on the Black Sea, analysts said. Moscow has also been racing to reopen ports along Ukraine’s occupied southern coast. Mr. Shoigu said that at least two ports, Berdiansk and Mariupol, have been cleared of mines left by retreating Ukrainian forces and are ready to resume operations.

Russia’s effort to establish a land route from Russia to Crimea was delayed by the bloody battle for Mariupol, where Ukrainian fighters held out for months despite being outnumbered and outgunned. In mid-May, they surrendered.

Capturing the devastated city represented a key step in fulfilling Mr. Putin’s vision of “Novorossiya” — a territory stretching across eastern and southern Ukraine along the Black Sea coastline to Crimea. The Russian president has called these “historically Russian lands,” and Moscow has moved quickly to “Russify” the population there, erecting statues of Lenin, introducing the ruble, rerouting internet connections to Russian servers and replacing Ukrainian cellular operators with Russian ones. Even the telephone country code has been changed to Russia’s.

Hennadii Lahuta, the Ukrainian head of Kherson’s regional military administration, said on Tuesday that the Kremlin planned to hold a referendum this fall, a step toward incorporating the region into Russia. Ukrainian officials have vowed to fight such a move, but so far their counteroffensive in the region has failed to retake much territory.

Rochan Consulting, which tracks developments in the war, said that while there was limited information about fighting in the south, its analysis suggests that the Ukrainian effort “may stall” because of a lack of tanks and infantry fighting vehicles. The British Ministry of Defense said on Wednesday that Ukraine’s counteroffensive was making limited progress.

Maj. Roman Kovalyov, a deputy commander of a Ukrainian military unit located northeast of Kherson, said in an interview last week that Ukraine was engaged more in disrupting actions than a full-fledged counteroffensive. “There are some settlements that we have liberated through our actions, but these were the fights of a tactical level,” he said.

At the same time, a clandestine battle has emerged inside the occupied regions, involving Kremlin loyalists, occupying Russian forces, Ukrainian partisans and the Ukrainian military.

On Tuesday morning, Ukrainian media posted video of what they said was an explosion at a cafe in the city of Kherson that served as a gathering place for people collaborating with the Russian forces. Russian state media described it as an act of “terror.”

It was the latest in a series of attacks targeting Russian supporters and proxies. And it comes amid reports — most impossible to independently verify — of Ukrainian guerrillas blowing up key bridges, targeting rail lines used by Russian forces and killing Russian soldiers on patrol.

Oleksiy Arestovych, an adviser to the Ukrainian president, said that there is an active but focused guerrilla movement in the south. “Partisans are fighting very actively,” he said in a broadcast on his YouTube channel.

Maj. Kovalyov, on the Kherson front, said Ukrainian forces were “fighting with what we have.”

“Generally most of the weapons that are being shipped to Ukraine go east,” he said. “We understand that here.”

Ivan Nechepurenko contributed reporting.