The Justice Department has appointed a special counsel to oversee a federal probe into possible ties between Russia and Donald Trump's 2016 presidential campaign.

Former FBI Director Robert Mueller will lead the investigation, the department said early Wednesday evening.

Democrats have been pushing for a special counsel from outside the Justice Department.

The appointment comes a day after news reports that ousted FBI Director James Comey crafted a memo detailing a February conversation between him and Trump that said Trump had asked him to shut down an FBI investigation into former Trump aide Michael Flynn.

Trump issued the following statement Wednesday: "As I have stated many times, a thorough investigation will confirm what we already know — there was no collusion between my campaign and any foreign entity. I look forward to this matter concluding quickly. In the meantime, I will never stop fighting for the people and the issues that matter most to the future of our country."

Information from the Associated Press was used in this report.