The war in Ukraine has prompted officials across Russia to scale back annual celebrations of Victory Day, the country’s most important national holiday, with more than 20 cities forgoing military parades and organizers calling off a popular nationwide march to honor veterans.

Security concerns were most often cited for the rash of cancellations of Tuesday’s events, but some analysts suggested that the unease had as much to do with fears about domestic disturbances.

It is an unprecedented step in a country where the parades, which commemorate the triumph of the Soviet Union over Nazi Germany in World War II, have become a signature event for President Vladimir V. Putin.

Over the years, he has cast the day not just as celebration of a historic victory but also of Russia’s present-day need to thwart the Western forces he says are still trying to destroy it. More recently, he has tried to wrap Ukraine into that narrative, falsely depicting it as a Nazi redoubt.

The country’s biggest parade, outside the Kremlin on Red Square, is still expected to be the usual display of raw military might, with row upon row of carefully choreographed soldiers marching amid weapons ranging from vintage tanks to intercontinental ballistic missiles. Mr. Putin is also scheduled to address the nation.

But outside of Moscow, a recent spate of drone attacks against military or infrastructure targets in cities like Sevastopol in Crimea, home port of the Black Sea fleet, as well as other attacks in the regions bordering Ukraine, have given officials pause. Not even the Kremlin has been immune, with two drones destroyed over Mr. Putin’s office last week.

Ukraine’s president, Volodymyr Zelensky, staked his nation’s own claim to the holiday, with an address on Monday drawing a parallel between World War II and the current war against Russian invaders. From now on, he said, May 9 will be called Europe Day, commemorating “the unity of all Europeans who destroyed Nazism and will defeat ruscism,” a Ukrainian term combining “Russian” and “fascism.”

“We fought then and we fight now so that no one ever again enslaves other nations and destroys other countries,” he said.

In Russia, various regional governors have cited security concerns in canceling Victory Day events. They have usually not gone into detail, but in Belgorod, a region bordering Ukraine, the governor suggested that slow-moving military vehicles and marching soldiers might make for inviting targets.

“There will be no parade in order not to provoke the enemy with a large amount of equipment and soldiers crowded in the center of Belgorod,” said the governor, Vyacheslav Gladkov. “The refusal to hold the parade is related to the safety of the residents of the region.”

Many areas have banned drone flights during the events, and the Readovka news outlet on Telegram reported that National Guard units were issued anti-drone weapons.

Igor Artamonov, the governor of the Lipetsk region, which is also near Ukraine, said his decision should not be misinterpreted.

“We are not afraid, we are not raising our hands,” he wrote on Telegram. “No neo-Nazi scum will be able to mar the great Victory Day. But we also have no right to put people at risk. It’s clear to everyone that parades are held in strictly defined squares at strictly defined times.”

The cancellation of the nationwide “Immortal Regiment” march, when ordinary Russians take to the streets to display pictures of their veteran forebears, is perhaps the most striking change. The Kremlin spokesman Dmitri S. Peskov said the march was canceled as a “precautionary measure” against possible attacks.

Some governors said they did not want to gather large numbers of people in the midst of war. But some analysts suggested that the Kremlin might be nervous that putting big crowds of Russians on the streets at such an uneasy time could lead to civil unrest, even with Russia’s draconian wartime laws against protests.

It might be especially volatile, analysts said, if thousands of people show up with pictures of those newly killed in the war, revealing the extent of a toll that the government has tried to conceal. Some portraits of soldiers killed in Ukraine were carried during last year’s celebrations, but the numbers were far smaller then, just two months into the fighting.

“People will not come out with portraits of their great-grandfathers,” Elvira Vikhareva, a political activist, wrote on Facebook. “People will come out with portraits of their fathers, sons and brothers. The regiment will not turn out to be ‘immortal,’ but very much mortal, and the scale will be visible.”

Whatever the reason, Russian officials have been trying to promote an alternative, suggesting that people upload the portraits to a special website or affix portraits of their veteran forebears to their vehicles and apartment windows.

Some local leaders far from Ukraine said they were canceling their parades in solidarity with frontline regions. In the Pskov region, home to a famous paratrooper division that has been devastated by the fighting and implicated in potential war crimes, Gov. Mikhail Vedernikov said that the sound of the fireworks would bother recuperating soldiers and that the money would be better spent on their needs.

Other regions planned to go forward with festivities, but on a smaller scale. In St. Petersburg, there will be no air force flyover, for example.

Some pro-war bloggers have groused that the men and equipment traditionally featured in many parades would be more useful at the front, shoring up the troubled war effort.

Governor Vedernikov suggested a twist, saying, “We must not celebrate victory, but do everything possible to bring it closer.”

Milana Mazaeva, Alina Lobzina and Shashank Bengali contributed reporting.