The widow of late Russian opposition leader Alexei Navalny vowed Tuesday that the rule of President Vladimir Putin will "definitely come to an end" shortly before he was sworn in for another six-year term, reports say. 

Yulia Navalnaya, speaking in a video posted to YouTube months after her husband mysteriously died at an Arctic penal colony, said "Our country is currently being led by a liar, a thief and a murderer, but this will definitely come to an end," according to Reuters. 

"Don't give up, truth will prevail," she added. 

During a ceremony inside the Grand Kremlin Palace on Tuesday, Putin, who has already led Russia for 25 years, placed his hand on the country’s constitution and promised to defend it, The Associated Press reports. 

RUSSIA’S KREMLIN PARADES WESTERN EQUIPMENT CAPTURED FROM UKRAINIAN ARMY AT EXHIBITION 

The U.S. State Department said Monday that it would not have a representative at the event. President Biden said in February that "Putin is responsible for Navalny’s death." 

Putin secured a fifth term in office in March, winning an election that featured no real opposition. 

"We certainly did not consider that election free and fair, but he is the president of Russia and is going to continue in that capacity," State Department spokesperson Matthew Miller said on Monday. 

PUTIN LIKELY DIDN’T INTEND FOR NAVALNY TO DIE IN FEBRUARY, US INTELLIGENCE AGENCIES ASSESS: REPORT 

Putin had walked away with 87% of the vote, according to Russia's election commission. He celebrated his victory over the smattering of token opposition candidates by saying at the time it was proof of the Russian people's "trust" in him. 

Russia's election commission also reported that Putin won over 76 million votes, setting a new record. 

Putin’s latest term as Russia’s president is set to last until 2030. 

Fox News’ Anders Hagstrom and Lawrence Richard contributed to this report.