The Wall Street Journal said on Thursday that it "vehemently denies" the spying allegations brought by Russia's intelligence service against its reporter.

"The Wall Street Journal vehemently denies the allegations from the FSB and seeks the immediate release of our trusted and dedicated reporter, Evan Gershkovich," a spokesperson for the WSJ said in a statement to ABC News. "We stand in solidarity with Evan and his family."

The FSB said it detained Gershkovich in the city of Ekaterinburg, in central Russia, and accused him of collecting "state secrets" on an enterprise belonging to Russia's military industrial complex on behalf of the United States.

Russia's FSB intelligence agency said on Thursday it had detained a journalist working for The Wall Street Journal on spying charges.

Russian state media cited an FSB statement saying Evan Gershkovich was detained in Ekaterinburg, a city in central Russia, and accusing him of collecting "state secrets" on an enterprise belonging to Russia's military industrial complex on behalf of the United States.

A criminal case has been opened against him, the officials said.

"It is established that Evan Gershkovich, acting on the instruction of the American side, was collecting information consisting of state secrets, about the activity of one of the enterprises of the Russian military industrial complex. He was arrested in Ekaterinburg during an attempt to receive secret information," Russian media said, quoting FSB officials.

Earlier reports from local media said that Gershkovich had been in Ekaterinburg reporting on the Wagner private military company.

Gershkovich is a reporter for the WSJ covering Russia, Ukraine and the former Soviet Union. He previously reported for Agence France-Presse and The Moscow Times, according to his WSJ profile. He also served as a news assistant at The New York Times.

-ABC News Tanya Stukalova and Patrick Reevell

The U.S. will support the creation of a special tribunal to prosecute top Kremlin officials for Russia's aggression toward Ukraine, State Department officials said Tuesday, marking a significant shift for the Biden administration and a notable step toward outlining what accountability on the international stage might look like after the conflict.

A department spokesperson said the administration envisioned the tribunal would take the form of an international court that is "rooted in Ukraine's judicial system" but ideally located in another European country.

The spokesperson added that such a mechanism would work to "facilitate broader international support and demonstrate Ukraine's leadership in ensuring accountability for the crime of aggression" as well as "maximize the chances of achieving meaningful accountability for the crime of aggression."

Ukraine and other Western countries have long called for a special tribunal, but until now, the U.S. has not publicly declared if it would support the creation of a new structure.

-ABC News' Shannon K. Crawford

At least two people were killed and 29 were injured Monday morning when a pair of long-range Russian missiles slammed into buildings in a city in eastern Ukraine, Ukrainian officials said.

The two S-300 Russian missiles hit administrative and office buildings, and private homes in Sloviansk, according to Pavlo Kyrylenko, the regional governor.

Sloviansk is in the Donetsk region of eastern Ukraine, where heavy fighting has been waged since the start of the war.

The missiles struck the city around 10:30 a.m. local time, Kyrylenko said.

He said the town of Druzhkivka in the Donetsk region was also targeted in Monday's missile attacks. Kyrylenko said a Russian missile "almost completely destroyed" an orphanage in Druzhkivka, but there were no immediate reports of casualties.

"Another day that began with terrorism by the Russian Federation," Ukrainian President Volodymyr Zelenskyy said in a statement.

Zelenskyy said Ukraine "will not forgive the torturing of our people."

"All Russian terrorists will be defeated," Zelenskyy said. "Everyone involved in this aggression will be held to account."

ABC's Will Gretsky

Russian President Vladimir Putin acknowledged Russian military losses from its ongoing invasion of Ukraine during his annual meeting with the federal security service Tuesday.

"Unfortunately, comrade officers, we know that there are losses in our ranks," Putin said.

Putin called on the FSB to provide "support" to the families of soldiers who have died in the war.

"We will always remember their heroism and bravery," he added.

Putin did not say how many soldiers have died in the war and the Russian Ministry of Defense hasn't disclosed an exact number of losses since September 2022 when Defense Minister Sergey Shoigu said just shy of 6,000 troops had died.

Secretary of State Antony Blinken and other State Department officials said Russia has likely suffered 200,000 injured or dead soldiers since the start of the war.

Putin also called on the FSB to make sure its border guard "undertake special efforts to control the Russian state border with Ukraine."

A "special group" is currently deployed at the Russia-Ukraine border, made up of border agencies, the FSB air arm, the Russian Armed Forces and the Russian National Guard, according to Putin.

"Your mission is to prevent any incursions by sabotage groups and stop any attempts to smuggle weapons and ammunition into Russia," Putin told the FSB board.

-ABC News' Tanya Stukalova and Anastasia Bagaeva