Comey also testified to the House Intelligence Committee that he had not information to support Trump's assertion he was under surveillance before he became president.
"I have been authorized by the Department of Justice to confirm that the FBI, as part of our counterintelligence mission, is investigating the Russian government's efforts to interfere in the 2016 presidential election," Comey said in his opening statement. "And that includes investigating the nature of any links between individuals associated with the Trump campaign and the Russian government and whether there was any coordination between the campaign and Russia's efforts."
Comey said he wouldn't be able to give many details of the investigation. In fact, the FBI doesn't normally confirm the existence of an ongoing investigation.
"But in unusual circumstances, where it is in the public interest, it may be appropriate to do so," Comey said.
He said the investigation could lead to charges.
"As with any counterintelligence investigation, this will also include an assessment of whether any crimes were committed," he said.
During questioning, Comey said he had no evidence of wiretapping at Trump Tower in New York, as the president asserted in a series of tweets earlier in the month.
"With respect to the president's tweets about alleged wiretapping directed at him by the prior administration, I have no information that supports those tweets," Comey told a U.S. congressional intelligence panel.