"The FBI must accelerate its investigation of the Russian connection with the Trump Administration," Pelosi said in a statement released Tuesday. "The American people deserve to know the full extent of Russia’s financial, personal and political grip on President Trump."
She said that Flynn's resignation reflected Trump's "poor judgment" and raised "grave answers" about the President's role in Flynn's conversations with Russia's ambassador to the United States.
"By what authority did Flynn act and to whom did he report?" Pelosi added.
Flynn resigned from his role as Trump's national security adviser late Monday night after questions arose about conversations he had before Trump's inauguration with Russian Ambassador Sergey Kislyak.
Current and former U.S. officials told several news outlets last week that Flynn and Kislyak discussed U.S. sanctions during a call before Trump took office. Those reports contradicted public statements made by members of Trump's administration, including Vice President Mike Pence, who denied that Flynn had any conversation about sanctions with Kislyak.
The New York Times reported in January that the FBI is leading an investigation into whether there were communications between associates of Trump's campaign and Russian officials, focusing on Trump allies Paul Manafort, Carter Page and Roger Stone.
Earlier in February, Pelosi called for an additional investigation into Trump's personal and business ties to Russia.
"I want to know what the Russians have on Donald Trump," she said.