A Moscow court has sentenced one of Russia's best-known opposition leaders, whose family live in the U.S., to 25 years in prison in what is widely seen a show trial.

Vladimir Kara-Murza is the most high-profile opponent of Russian President Vladimir Putin to be jailed since Alexey Navalny.

Kara-Murza's extraordinarily harsh sentence is one of the lengthiest any opposition figure has received under Putin and illustrates how repressive Russia has become during the war in Ukraine, reverting to something much closer to the USSR where no opposition is tolerated.

Kara-Murza was convicted of treason, as well as "discrediting Russia's armed forces," a new law that effectively criminalizes criticizing the war in Ukraine. He was also convicted of belonging to a banned organization. The charges are widely seen as politically motivated.

Kara-Murza is one of Russia's best-known pro-democracy figures and a veteran critic of Putin.

Kara-Murza, who holds both British and Russian citizenship, spent many years living in the United States and his wife and children still live in Virginia. He was close to the late U.S. Sen. John McCain, who championed human rights in the former Soviet Union.

Dozens of journalists and Western diplomats attended the court hearing on Monday, including the U.S. ambassador who read out a statement condemning the sentence.

"We support Mr. Kara-Murza and every Russian citizen to have a voice in the direction of their country. Mr. Kara-Murza and countless other Russians believe in and hope for a Russia where fundamental freedoms will be upheld. And we will continue to share those hopes and work for that outcome," Amb. Lynne Tracy said.

Kara-Murza previously has survived being poisoned not once but twice. In 2015 and then again in 2017, he suffered organ failure after being exposed to an unknown toxin. Independent researchers later linked the poisoning to the same team of FSB poisoners who targeted Navalny.

He chose to return to Russia after the war began, believing it was important to continue to campaign for freedom in his country and has been an outspoken critic of the invasion.

His trial was held entirely behind closed doors, but a letter containing his closing statement to the court has been released to reporters.

"I only blame myself for one thing," Kara-Murza said in the statement. "I failed to convince enough of my compatriots and politicians in democratic countries of the danger that the current Kremlin regime poses for Russia and for the world."

"Criminals are supposed to repent of what they have done. I, on the other hand, am in prison for my political views. I also know that the day will come when the darkness over our country will dissipate.

-ABC News' Patrick Reevell

The parents of Wall Street Journalist journalist Evan Gershkovich spoke in an interview with with the paper Friday, the first time since their son was detained in Russia in March.

Mikhail and Ella Gershkovich, who were born in the Soviet Union and married after emigrating to the U.S. separately in 1979, talked about how much he wanted to work for the Journal and cover Russia.

"He said I'm just one of the few left there," Ella Gershkovich, his mother, said of his time working in Russia during the Ukraine war.

The couple said their family is keeping hope that their son will be returned.

The couple said their family is keeping hope that their son will be released.

"It's one of the American qualities we absorbed. Be optimistic, believe in happy ending. That's where we stand right now, but I am not stupid. I understand what's involved, but that's what I choose to believe," Ella Gershkovich said.

-ABC News' Ellie Kaufman

Russian forces shelled Slovyansk, a city in the Donetsk region of Ukraine, Friday, Andrii Yermak, the head of the office of the President of Ukraine, said on Telegram.

At least seven explosions were heard in the city in the area near a school, and three buildings were struck, Yermak said. Russia hit three five-story buildings in the attack, he added.

Fifteen people, including one child, were killed and 24 people have been wounded, officials said Sunday.

Ukrainian President Volodymyr Zelenskyy shared a video of the attack on his Telegram page and condemned Russian forces.

He said there are still people trapped in the rubble.

"The evil state once again demonstrates its essence, just killing people in broad daylight, [and] ruining, destroying all life," he said.

-ABC News' Oleksiy Pshemyskiy and Ellie Kaufman

Country singer Brad Paisley visited Ukraine for the first time on Wednesday and met with President Volodymyr Zelenskyy to see firsthand what's happening in the war-torn country, according to Ukrainian fundraising platform UNITED24.

Paisley, who serves as a global ambassador for UNITED24 and its campaign to help rebuild Ukraine, performed his song "Same Here" while in St. Michael’s Square in Kyiv.

Paisley, who went with a bipartisan U.S. Senate delegation, also played for American troops in Poland, UNITED24 said.

“It’s an emotional experience seeing all of this firsthand," Paisley said during a press conference. "For me, looking around this city and being here for the first time, I’m absolutely struck by the resilience of life and the beautiful nature of the way this city is trying to thrive in the middle of conflict."

U.S. Secretary of State Antony Blinken urged the Kremlin to release imprisoned Wall Street Journal reporter Evan Gershkovich in a phone call Sunday with his Russian counterpart, according to a State Department spokesperson.

Blinken spoke with Russian Foreign Minister Sergey Lavrov, conveying the United States' "grave concern" over the "unacceptable detention" of a U.S. citizen, according to Vedant Patel, a deputy spokesperson for the State Department.

"The secretary called for his immediate release. Secretary Blinken further urged the Kremlin to immediately release wrongfully detained U.S. citizen Paul Whelan," said Patel, referring to the American held in Russia on espionage charges since 2018.

According to a read out of the phone call released by the Kremlin, Lavrov emphasized that Gershkovich "was taken red-handed while trying to obtain classified information, collecting data constituting a state secret under the guise of journalistic status."

"In the light of the established facts of illegal activity of a U.S. citizen, of whose detention the U.S. Embassy in Moscow was notified in accordance with the established procedure, his further fate will be determined by the court," the Kremlin said in a statement.

The Kremlin said that during the conversation, Lavrov emphasized officials in Washington and the Western media are "escalating the hype with the clear intention of giving this case a political coloring."

Blinken and Lavrov also spoke of the "importance of creating an environment that permits diplomatic missions to carry out their work," according to Patel.