MOSCOW — Russian anti-corruption campaigner Alexei Navalny slammed the latest court action against him Friday as one more trumped-up political case by the government of President Vladimir Putin.

The case — involving charges of criminal libel against an elderly war veteran — was a “PR trial” used to smear him, said the jailed opposition leader, who was appearing in court for the second time this week. Navalny had been sentenced Tuesday to two years and eight months in prison after authorities accused him of breaching probation rules.

“The Kremlin needs headlines: ‘Navalny slandered a war veteran,’ ” he said, according to local media present at the hearing.

Navalny, whose return to Russia and jailing triggered the toughest crackdown on peaceful opposition since Soviet times, also faces a separate case in which he is accused of embezzlement, carrying a sentence of up to 10 years.

Navalny alleges that Putin ordered his murder in a chemical nerve-agent attack in August. He survived but spent nearly five months in Germany receiving medical treatment.

Riot police have detained more than 10,000 protesters at peaceful demonstrations calling for Navalny’s release in more than 100 cities across Russia since Jan. 23. Police cells are so full that there is nowhere to put the detained protesters, with independent local media reporting that some were kept in police vans lacking food and water for two days.

On Thursday, the head of Navalny’s regional headquarters, Leonid Volkov, called off protests until spring or summer.

Russia’s treatment of Navalny has further strained Russian relations with the West, with the Kremlin brushing off Western calls to free him and to investigate the poisoning attack. Russia’s Foreign Ministry on Friday expelled three European diplomats whom it accused of “participating” in unauthorized rallies in support of Navalny. The diplomats were from the German Embassy in Moscow and the Swedish and Polish consulates in St. Petersburg.

German Foreign Minister Heiko Maas said the move was unjustified and would not go unanswered. Sweden’s Foreign Ministry rejected the claim that its diplomat took part in a protest, and it threatened to retaliate. Poland’s Foreign Ministry said its diplomat was performing her duties and called on Russia to reverse the decision, also threatening retaliation.

European Commission foreign policy chief Josep Borrell, in a Moscow meeting with Russian Foreign Minister Sergei Lavrov, called for Navalny’s release. He also urged Russian authorities to investigate the poisoning.

Lavrov complained that the European Union is “not a reliable partner,” warning that any further deterioration of relations would be “fraught with negative and highly unpredictable consequences.”

Kremlin spokesman Dmitry Peskov hit back Friday at President Biden’s comment Thursday that Washington would no longer be “rolling over” in the face of what he described as Russia’s provocative actions. Peskov called the remarks “very aggressive and unconstructive rhetoric.”

“We will not heed such statements, any kind of patronizing statements,” Peskov said, adding that the Kremlin hoped to continue talking to the White House “despite the huge number of differences.”

Friday’s libel case involves a propaganda video aired in June on Kremlin mouthpiece Russia Today promoting a nationwide vote in June and July on changes to the Constitution enabling Putin to stay in office until 2036. (The changes were passed.)

In the video, Russian celebrities and sports figures supported the amendments. Navalny tweeted that the participants were “corrupt hacks.” Among them was a 94-year-old World War II veteran, Ignat Artemenko. Russia’s Investigative Committee alleged that he suffered heart problems after finding out about Navalny’s tweet.

Navalny said the case against him was orchestrated by the state, using Artemenko.

“I’m looking at what is happening right now, and it is disgusting,” he said. “It’s not just that you are using this poor man as a puppet. The question is: Who are the fascists? Who are the political whores? His relatives are trading on him to get money and are bullying him.”

He said the goal of the regime’s 2020 campaign to promote changes in the Constitution was to make Putin president for life.

Artemenko appeared in the hearing via video from his apartment in northwest Moscow, where there were several other people whose identities were not immediately clear. Judge Vera Akimova said a female judge was present in the apartment.

“Is she telling him what to say?” Navalny asked, demanding that the court video show all the people present in the apartment.

The judge countered that it was not technically possible.

“Please turn the camera around,” Navalny insisted. “Show us who is conducting this trial.”

The war veteran, who was wearing his medals, made a brief statement that he was upset when he learned about Navalny’s comments and felt the need to defend his dignity. He called for a public apology from Navalny.

Then he told prosecutor Yekaterina Frolova that he was not feeling well, “and I ask you to stop the questions.” Navalny’s attorneys were not given the opportunity to cross-examine Artemenko.

Navalny complained that Artemenko appeared to be reading from a piece of paper that had been given to him, including the phrase that he was not well and wanted to take no more questions.

Akimov said an ambulance had to be called for Artemenko’s apartment. Frolova requested that the court transcript record that Navalny was to blame for causing the veteran to fall ill.

Artemenko’s status as a war veteran, belonging to a revered group in Russia, may be designed to undermine Navalny’s swell of support, with pro-Kremlin presenters describing him as rehabilitating Nazism.

Navalny later clashed with Igor Kolesnikov, Artemenko’s grandson. Kolesnikov said neither he nor his grandfather filed the complaint about the alleged libel and could not say who did.

This contradicted the testimony of the war veteran’s nurse, Zina Temurova, who said Kolesnikov and Artemenko wrote the complaint together.

Navalny said it was clear that the investigator in the case wrote the complaint and that it amounted to a fabrication. The prosecutor immediately called for an adjournment, and the judge adjourned the hearing until Feb. 12.

More than 8,000 riot-police officers flooded central Moscow after Tuesday’s jail verdict, according to the Telegram channel Baza. They forced young protesters into corners and against walls before moving in, beating them with truncheons and dragging them away.

Political analyst Tatiana Stanovaya of the R. Politik political-risk consultancy tweeted that the aim of Russia’s security services was “to destroy Navalny and to demonstrate that no move aimed against the security services would remain unpunished.”

“The Kremlin has plenty of other potential criminal charges it can bring against Navalny,” she wrote. “The goal is to make Navalny — and others — realize that they face the prospect of spending the rest of their lives behind bars.” She said the crackdown would result in ramped-up pressure on liberal media, nongovernmental organizations, opposition activists and citizens.

Navalny’s decision to fly home to Russia, knowing the regime would probably jail him, has marked him as Putin’s only genuine political rival. Jailing him for years silences him and could leave his opposition movement adrift, struggling to maintain the momentum of protests through spring and summer over parliamentary elections due in September.

“These are the biggest repressions modern Russia has seen. The penal system is suffocating with detainees. Journalists are arrested. What is happening to Russia?” Echo of Moscow Radio asked Kremlin spokesman Peskov on Thursday, reflecting the alarm many feel about the scale of the crackdown.

“There are no repressions,” Peskov replied. “There are police measures against those who break the law.”

Reuters cited two sources Thursday close to the Kremlin as saying that authorities were ready for tougher measures across Russia to stop the protests and break the opposition.