Former FBI Director James Comey fiercely defended the bureau's counterintelligence investigation into President Trump's 2016 campaign after the New York Times reported on Thursday the FBI sent an undercover investigator to meet with a Trump campaign adviser.

During an interview with a Los Angeles radio station, Comey argued the FBI's actions, which have come under fire by GOP investigators concerned about a politically motivated operation to undermine Trump, were restrained and even flawless.

“Really? What would you have the FBI do? We discover in the middle of June of 2016 that the Russians were engaged in a massive effort to mess with this democracy to interfere in the election. We're focused on that and at the end of July we learn that a Trump campaign adviser — two months earlier, before any of this was public — had talked to a Russian representative about the fact that the Russians had dirt on Hillary Clinton and wanted to arrange to share it with the Trump campaign,” Comey told KNX 1070 AM on Friday.

"What should the FBI do when it gets that information? It should investigate to figure out whether any Americans are hooked up with this massive interference effort," he added. "And that's what we did. And as I said earlier, we should have been fired if we didn't. And Republicans ought to breath into a paper bag. There's no way you would do other than what we did, which was use limited tools to try to understand: Is this true? And that's what the investigation was about."

Comey oversaw the FBI when the bureau began its original counterintelligence investigation, called Crossfire Hurricane, in July 2016. It was prompted by Australian diplomat Alexander Downer informing the U.S. government that Trump campaign adviser George Papadopoulos told him Russia had stolen emails related to Hillary Clinton, Trump's Democratic rival in the 2016 election.

The Times report revealed that a woman who said her name was Azra Turk posed as an assistant to Stefan Halper, an American professor at Cambridge University and informant for the FBI looking into ties between the Trump campaign and Russia. Turk asked Papadopoulos point blank if Trump's campaign was working with the Russians at a bar in London in September 2016.

Calling the timing of the Times report "no coincidence," Rep. Mark Meadows, a lead GOP investigator, said the "leaks" show the FBI feels threatened by an investigation by Attorney General William Barr into the origins of the Trump-Russia investigation. Barr, who recently said "spying did occur" on Trump's presidential team, testified last week that he is "working very closely” with Justice Department Inspector General Michael Horowitz, who has been looking into possible Foreign Intelligence Surveillance Act abuse.

[Related: Comey team may have used confidential sources prematurely, ex-FBI intel official says]

The FBI not only used undercover informants to keep tabs on Trump campaign officials with suspicious ties to Russia, but also electronic surveillance.

In February 2018, the House Intelligence Committee, then led by Chairman Devin Nunes, R-Calif., released a memo asserting the so-called Trump dossier, which contained unverified claims about Trump's ties to Russia, was used by the FBI to help obtain a FISA warrant and three renewals to spy on one-time Trump campaign adviser Carter Page. But key information, including its author's anti-Trump bias and Democratic benefactors, was left out. Republicans have often cited the use of the dossier as misinformation used to improperly monitor Trump and his campaign during the months leading up to the 2016 presidential election while Democrats argued in a rebuttal memo that the FISA process was not abused and the Justice Department and FBI "met the rigor, transparency, and evidentiary basis needed to meet FISA's probable cause requirement."

GOP outrage over alleged spy abuse extends all the way up to the White House. In a recent interview on Fox News, Trump said Comey, whom he fired from the FBI in May 2017, "probably was one of the people leading the effort on spying" on his 2016 campaign and hinted at a coming document release that would expose the truth.

Comey has vehemently disagreed with the use of the word "spying" to describe the FBI's efforts. "When I hear that kind of language used, it’s concerning because the FBI, the Department of Justice conduct court-ordered electronic surveillance,” Comey said at the Hewlett Foundation's Verify Conference last month. “I have never thought of that as spying.”

[Read more: FBI Director Wray contradicts his boss AG Barr over 'spying' on Trump: 'Not the term I would use']

The FBI's counterintelligence was wrapped into special counsel Robert Mueller's investigation, which recently wrapped up. Mueller said in his report that his team could not establish criminal conspiracy between the Trump campaign and the Kremlin, but did not make a conclusion about whether Trump obstructed justice. Barr said he and Deputy Attorney General Rod Rosenstein determined that there was inconclusive evidence to establish an obstruction crime took place, but Democrats argue Mueller left the question open to Congress to investigate and decide.