(CNN) The Justice Department has started to probe a series of stock transactions made by lawmakers ahead of the sharp market downturn stemming from the spread of coronavirus, according to two people familiar with the matter.

The inquiry, which is still in its early stages and being done in coordination with the Securities and Exchange Commission, has so far included outreach from the FBI to at least one lawmaker, Sen. Richard Burr, seeking information about the trades, according to one of the sources.

Burr, the North Carolina Republican who heads the Senate Intelligence Committee, has previously said that he relied only on public news reports as he decided to sell between $628,000 and $1.7 million in stocks on February 13. Earlier this month, he asked the Senate Ethics Committee to review the trades given "the assumption many could make in hindsight," he said at the time.

There's no indication that any of the sales, including Burr's, broke any laws or ran afoul of Senate rules. But the sales have come under fire after senators received closed-door briefings about the virus over the past several weeks — before the market began trending downward. It is routine for the FBI and SEC to review stock trades when there is public question about their propriety.

In a statement Sunday to CNN, Alice Fisher, a lawyer for Burr, said that the senator "welcomes a thorough review of the facts in this matter, which will establish that his actions were appropriate."

"The law is clear that any American -- including a Senator -- may participate in the stock market based on public information, as Senator Burr did. When this issue arose, Senator Burr immediately asked the Senate Ethics Committee to conduct a complete review, and he will cooperate with that review as well as any other appropriate inquiry," said Fisher, who led the Justice Department's criminal division under former President George W. Bush.

Congress passed the Stock Act in 2012, which made it illegal for lawmakers to use inside information for financial benefit.

Under insider trading laws, prosecutors would need to prove the lawmakers traded based on material non-public information they received in violation of a duty to keep it confidential.

Burr's committee has received periodic briefings on coronavirus as the outbreak has spread, but the committee did not receive briefings on the virus the week of Burr's stock sales, another source familiar with the matter told CNN earlier this month.

Spokespeople for the Justice Department, the FBI and the SEC declined to comment.

In an interview with CNBC on Monday morning, SEC Chairman Jay Clayton would not confirm the inquiry, but sent a warning about trading with private information.

"Anyone who is privy to private information about a company or about markets needs to be cautious about how they use that private information. That's fundamental to our securities laws and that applies to government employees, public officials, etc, and the Stock Act codifies that," Clayton said.

Burr's sales represent a sizable share of his portfolio of stocks, according to his latest Senate financial disclosure documents filed in May 2019, although exact numbers aren't possible because lawmakers only report trades as a range of dollar values.

Several other senators from both parties also sold and bought stock ahead of the market downturn that resulted from the coronavirus pandemic, although it's not clear who else the Justice Department is looking at and no other senator said they have been contacted by law enforcement. Burr is the only lawmaker to have asked for an Ethics Committee review.

GOP Sen. Kelly Loeffler of Georgia and her husband sold 27 stocks valued between $1.275 million and $3.1 million from January 24 through February 14, according to Senate records.

They also purchased three stocks at a value of $450,000-$1 million, including shares in Citrix, a software company that's gained approximately 15% in value since Loeffler and her husband bought the stock last month.

Loeffler, who was appointed to her seat in December and was sworn in in early January, has denied having any knowledge of the stock sales, saying she uses a third-party financial adviser and did not learn of the trades until later. Loeffler's husband, Jeffrey Sprecher, is chairman of the New York Stock Exchange.

A Loeffler spokesperson confirmed Loeffler has not been contacted by the FBI and said the senator "has acted in accordance with the letter and the spirit of the law."

Others who traded relatively smaller amounts or sold fewer stocks than Burr and Loeffler have also faced public scrutiny.

Stock sales were reported last month by Sens. Dianne Feinstein, a California Democrat, and Jim Inhofe, an Oklahoma Republican. Both Feinstein's and Inhofe's offices said the senators had not been contacted by the FBI.

Feinstein herself did not sell any stock, according to Senate records. Her husband sold between $1.5 million and $6 million in stock of Allogene Therapeutics, a biotech company, in January and February. Feinstein said earlier this month that she has no involvement in her husband's financial decisions.

"I have no input into his decisions. My husband in January and February sold shares of a cancer therapy company. This company is unrelated to any work on the coronavirus and the sale was unrelated to the situation," she said in a statement.

Inhofe sold five stocks, worth between $180,000 and $400,000, in January, and another for $50,000-$100,000 in February. But he said in a statement earlier this month that he had no involvement in his investment decisions.

This story has been updated with additional information.