Jill Stein is asking the Justice Department to investigate the "integrity" of the U.S. electoral system to address "grave concerns" that arose from the Green Party's recount push in three swing states.

In a letter addressed to Attorney General Loretta Lynch, Stein's attorney wrote Friday of the "susceptibility to malicious interference and poor performance" found in voting machines in Wisconsin, Michigan and Pennsylvania — three states won by Republican Donald Trump.

"The attempted recount process has uncovered that voting machines relied on in these states and across the country are prone to human and machine error, especially in under-resourced black and brown communities, and vulnerable to tampering and hacking," the letter reads. "The recount also found that the states' efforts to protect their systems may be insufficient, particularly in low-income communities and communities of color. Each of these grave concerns warrants federal intervention."

The letter cites "cyber vulnerabilities" as a major concern, and criticizes FBI Director James Comey for falsely indicating to Congress that mass corruption of voting machines can't happen because they are not connected to the Internet. Stein's lawyer wrote that the administrator of the Wisconsin Elections Commission testified under oath that some voting machines connect to the Internet. The letter also warns that some voting machines that are not connected to the Internet, were connected to others that were, which could pose a cybersecurity risk.

Human error was also uncovered in the recount process, the letter claims.

To help safeguard against these problems in the future, the letter to Lynch calls for all jurisdictions to use paper-ballot based systems and for there to be automatic audits to verify the results of every election. The costs of funding a recount, Stein's lawyer said, can be "prohibitive."

"Our representative democracy is founded on voting for our elected representatives," the letter reads. "It is both a paramount civic duty and a fundamental right. Americans need to be confident that our votes are counted accurately."

U.S. intelligence officials have blamed Russia for meddling in the electoral process by leaking hacked emails from Democrats. Russian President Vladimir Putin may have personally been involved in working to undermine Democrat Hillary Clinton's campaign, some U.S. officials have said. But there has not been any indication by U.S. officials that voting machines were tampered with by Russian hackers.

Stein's recount campaign, in which she raised millions of dollars, resulted in only one successful electoral review in Wisconsin. It added 162 votes to Trump's tally.

Stein won only 1 percent of the popular vote nationwide.