Since the invasion of Crimea in 2014, Kremlin critics say they see a violent edge to Russia’s patriotic fervor, creating danger for those who dissent. (Alexander Aksakov/Getty Images)

Days after Russian opposition leader Boris Nemtsov was killed at the Kremlin’s doorstep, his grieving allies say that a year of dark accusations of treason and fascism laid the groundwork for his death.

No suspect has been identified in the highest-profile assassination to occur during President Vladimir Putin’s 15 years in power, and authorities say they are searching wide for motives. But Nemtsov’s friends say there is a violent undertone to the patriotic fervor that has overtaken Russia since it annexed Ukraine’s Crimean Peninsula a year ago. Now anyone who criticizes the Kremlin risks being painted as an enemy of the state. Nemtsov’s killing may be only the beginning, they say.

Their anxiety has been heightened because the killing took place in one of Russia’s more highly secure areas. To Putin critics, who generally think Nemt­sov’s death was politically motivated, the toxic rhetoric of the past year has unleashed furies beyond the Kremlin’s control or an even scarier conspiracy is afoot.

[Read: Echoes of Stalin in the murder of a Putin foe]

Putin denies any connection to the killing, and his spokesman said it was a “provocation” intended to undermine the Kremlin.

Putin gave official sanction to the sharpened tone against the political opposition a year ago, many of his critics say, when he warned that “a fifth column” and “national traitors” were undermining Russia from within. Banners soon hung in the heart of Moscow that said Nemtsov and fellow opposition leaders were “aliens among us.” And Russia’s powerful state-run television stations were quickly suffused with grim tales of Western-backed crimes against their countrymen in Ukraine, further fueling popular disbelief that any Russian could support the other side.

With Putin’s approval ratings parked near record highs at 86 percent, the fraction of Russians who fall outside of the mainstream feels increasingly vulnerable. Many hard-right nationalists have gone to fight in eastern Ukraine — and Kremlin critics fear what will happen if they continue their battle at home. Some wonder whether rogue groups are responsible for Nemtsov’s killing.

“I don’t remember such a level of hatred as we have now in Moscow,” Nemt­sov wrote last year, months before he was cut down by four bullets as he walked steps from the Kremlin walls.

“People are being set against each other, provoking a massacre. All this hell cannot end peacefully,” he wrote. “The vampire wants blood, and not only that of Ukrainians.”

Soon after the annexation of Crimea, it was difficult to turn on a television without hearing about fresh atrocities in Ukraine. On Russia’s most popular television programs — beamed nationwide in a country where 90 percent of people get their news from TV — tales of violence became routine.

Ukrainian volunteer forces­ “came to villages and small towns. They were raping girls, women and grandmothers, young and old, and they were telling them, ‘You should not give birth to Russians,’ ” Russian lawmaker Nikolai Kharitonov told a talk show in January, offering no evidence to support his accusation. On a separate show, viewers were told that Ukrainian children were being taught to hunt birds whose plumage comes in Russia’s national colors.

Prominent Russians who expressed sympathy with Ukraine have been accused of taking money from the West to plot revolution in Russia. When popular rock musician Andrey Makarevich performed in eastern Ukraine for an audience of Ukrainian refugees, a lawmaker accused him of “partnering with fascists.” Then he was shut out of Russian perform­ances. Later, he was featured on a program called “13 Friends of the Junta.”

State-run television is a key linchpin of the Kremlin’s strategy to foster anti-Western sentiments, analysts say. Trusted far more than Soviet-era broadcasts ever were, networks transmit a skillful blend of fact and spin, unrelentingly promoting the idea that Russia is a nation under attack from inside and out. Their budgets have been bolstered this year, even as other state agencies have been forced to cut.

Although occasional voices of dissent do make it onto television networks, such guests are usually presented in a way that undermines their credibility.

“You try to start answering, then you get interrupted and people start shouting at you,” said Robert ­Pszczel, the head of the NATO Information Office in Moscow, who regularly appears on Russian talk shows as the token Westerner.

“You think differently; therefore, you don’t really have full rights,” he said.

Ahead of a nationalist rally held less than a week before Nem­tsov’s death, slick promotions ran constantly on federal news channels imploring people to turn out. The protest, held on the first anniversary of Ukrainian president Viktor Yanukovych’s ouster, was billed as an “anti-Maidan” rally to prevent what happened in Kiev from repeating in Moscow.

Nemtsov’s face was on some of the posters at the rally, condemned as a supporter of the protests in Ukraine. Moscow police said 35,000 people attended the rally, where they sang World War II-era songs about fighting fascism and compared President Obama to Adolf Hitler.

Public expressions of violence have become common. Russia’s most prominent news anchor, Dmitry Kiselyov, reminded audiences that their nation was the only one capable of turning the United States into “radio­active ash.” A news program in St. Petersburg showed viewers how long it would take Russian soldiers to overrun European capitals. Boasts of Russia’s nuclear prowess are common from ordinary people at the gym all the way to the highest reaches­ of power.

And on a goodwill trip by Russian movie star Mikhail Porechenkov to visit pro-Russian rebels in eastern Ukraine, he casually shot a heavy machine gun at Ukrainian army positions in the Donetsk airport. He later claimed the rounds were blanks.

Now many Kremlin critics deeply fear the future.

“They openly said at the anti-Maidan rally that their aim was to destroy the fifth column in Russia. Who knows what they meant, physically or through words,” said Vladimir Ryzh­kov, a close political ally of Nemtsov’s who said that dissenters were far more vulnerable now than they were for much of the Soviet era.

“It’s much more hot, much more unpredictable, much more violent, and the threat is from everywhere,” he said.

Some people are hardening themselves for the worst.

“Now there are no rules whatsoever,” said Yevgenia Albats, a prominent opposition journalist who was one of Nemtsov’s closest friends. “This constant calling to get rid of the fifth column, of those who betrayed the country, definitely may inspire people to go for this killing.”

Albats, who was singled out in a darkly conspiratorial segment on a national news show last year, said that people like her had no choice but to contemplate being killed.

“You try to prepare, put your papers in order,” she said.