The FBI has launched an investigation into claims by the Trump campaign that it was the target of a hacking attempt linked to the Iranian government. The FBI confirmed the investigation on Monday, though it did not specifically name Trump or Iran.

A Trump campaign spokesperson told the BBC that the documents were unlawfully obtained by “foreign sources hostile to the United States.” Iranian officials have denied involvement, and the U.S. government has not officially accused Iran.

According to CBS News, which cited sources familiar with the investigation, the FBI is also probing whether Iranian hackers attempted to infiltrate the Biden-Harris campaign. This follows a report by Microsoft indicating that Iranian hackers targeted an unnamed U.S. presidential campaign in June with spear-phishing emails designed to appear trustworthy and trick recipients into clicking on malicious links.

On Saturday, Trump claimed that the hackers only accessed publicly available information. The FBI reportedly began its investigations in early summer after both campaigns encountered phishing attempts.

The Washington Post reported that three Biden-Harris campaign staff members were targeted by phishing emails shortly before President Joe Biden announced he was leaving the race. A Harris campaign spokesperson said they were vigilant against cyberthreats and were unaware of any security breaches.

Democratic Congressman Adam Schiff has called on the FBI to reveal what it knows about the hacking attempts, criticizing the slow response to Russian interference in the 2016 election. Congressman Eric Swalwell has requested a briefing from the Department of Homeland Security regarding the alleged hack of Trump’s campaign, emphasizing that while Trump’s actions in the past have been questionable, foreign interference should never be tolerated.

The investigation follows warnings of an Iranian plot to assassinate Trump, unrelated to an attempted shooting in Pennsylvania last month. On Tuesday, the U.S. Justice Department charged a Pakistani man with ties to Iran with plotting to assassinate U.S. officials, potentially including the former president.