U.S. intelligence recently detected an Iranian plot against former President Donald Trump, U.S. officials tell CBS News — although intelligence officials haven't found any ties between Saturday's failed attempt on Trump's life by 20-year-old shooter Thomas Matthew Crooks and any foreign or domestic accomplice.

Upon learning about the heightened threat, the National Security Council contacted the Secret Service. In response, the Secret Service increased resources and assets for Trump's protection in June. Additional resources including Counter Assault Team personnel, counter sniper team personnel, drones and robotic dogs were provided.

CBS News has learned the intelligence goes beyond chatter and involves human source intelligence obtained by the U.S.

It's not clear how far along the Iranian plot was when it was detected, but Trump has long been a point of ire for the Iranians, most notably for directing the 2020 airstrike that killed top Iranian commander Gen. Qasem Soleimani.

"As we have said many times, we have been tracking Iranian threats against former Trump administration officials for years, dating back to the last administration," said NSC spokesperson Adrienne Watson. "As we have said many times, we have been tracking Iranian threats against former Trump administration officials for years, dating back to the last administration. These threats arise from Iran's desire to seek revenge for the killing of Qassem Soleimani. We consider this a national and homeland security matter of the highest priority."

The Secret Service said it could not comment on any specific threats, but said it "takes threats seriously and responds accordingly."

"The Secret Service and other agencies are constantly receiving new potential threat information and taking action to adjust resources, as needed," Secret Service spokesman Anthony Guglielmi said in a statement.

Iranian officials have rebuffed the allegations as "malicious," with foreign ministry spokesman Nasser Kanani saying Wednesday that Tehran "strongly rejects any involvement in the recent armed attack against Trump."

Iran's mission to the United Nations, meanwhile, called the allegations of previous plotting against Trump "unsubstantiated and malicious."

The news came as the Republican National Convention is underway in Milwaukee. On Monday night, Trump made his first public appearance since Saturday's shooting, with a bandage over his right ear, to mark his formal nomination and selection of Ohio Sen. JD Vance as his running mate.

"We do not comment on President Trump's security detail," a Trump campaign spokesperson said Tuesday.

Secret Service and the Department of Homeland Security as a whole are under close scrutiny after Saturday's failed assassination attempt. The shooter injured Trump, killed one spectator and critically injured two others before a Secret Service sniper shot and killed him.