The Latvian intelligence services had previously charged Kasem with spying for Russia.
The journalist was placed in the Riga Central Prison.
“I regard the use of criminal repression against journalist Marat Kasem as an encroachment on freedom of speech, and a violation of Latvia’s international obligations in the field of protecting the rights of journalists,” Moskalkova wrote in her Telegram.
The Russian Ombudsman appealed to the UN High Commissioner for Human Rights with a request to pay attention to the incident and take action as part of her mandate to protect the rights of Kasem.
Earlier it became known that Marat Kasem was detained by the special services of Latvia in Riga.
Dmitry Kiselyov, director general of the Rossiya Segodnya media group, said that Kasem's detention was unlawful and absurd.
The head of the Union of Journalists of Russia, Vladimir Solovyov, called Kasem's detention a flagrant violation of all principles of freedom of speech.
On January 6, a rally will take place near the Latvian Embassy in Moscow in support of the editor-in-chief of Sputnik Lithuania detained in Riga.