The US received intelligence in recent weeks about a plot by Iran to try to assassinate former president Donald Trump, American news organisations reported on Tuesday.
"We have been tracking Iranian threats against former Trump administration officials for years, dating back to the last administration," National Security Council spokeswoman Adrienne Watson said in a statement.
"These threats arise from Iran's desire to seek revenge for the killing of Qassem Suleimani. We consider this a national and homeland security matter of the highest priority."
Suleimani, head of Iran's Islamic Revolutionary Guard Corps' foreign operations, was assassinated in a US drone attack near Baghdad International Airport early in 2020.
There was no indication that the 20-year-old suspect in the shooting of Mr Trump on Saturday, Thomas Mathew Crooks, was connected to the plot, Ms Watson said of the continuing investigation.
The US Secret Service and the Trump campaign were made aware of the plot before Saturday's rally, a national security official told CNN, which first reported the news.
"We are ... consistently in touch with the agencies overseeing the security details of these former officials to share evolving threat information on a timely basis and to reinforce President [Joe] Biden's directive that they receive every resource, capability and protective measure required to address those evolving threats," Ms Watson said.
The agency has come under scrutiny in recent days after the suspected gunman gained access to a roof and fired directly at Mr Trump, grazing his ear, killing a rallygoer and critically injuring two others.
Secret Service spokesman Anthony Guglielmi said at the weekend that the "US Secret Service quickly responded with protective measures".
The agency's director, Kimberly Cheatle, will testify on the shooting at a House of Representatives oversight committee hearing next Monday.
Ms Watson said the Secret Service and Homeland Security Department would brief about "additional measures that have been implemented in recent weeks".
Mr Guglielmi told CNN that the agency had recently “added protective resources and capabilities to the former president’s security detail”.
The Secret Service did not immediately respond to a request for comment from The National.
Iran has been charged with trying to attack Mr Trump's former national security adviser John Bolton and former US secretary of state Mike Pompeo in assassination plots.
NBC News says they continue to have security details due to the threats.
The US in January imposed sanctions on a network of people linked to the Iranian government for their alleged involvement in assassination attempts against dissidents and opposition activists abroad.
The network is believed to have carried out several assassinations, kidnappings and other operations – including in the US – “in an attempt to silence the Iranian regime's perceived critics”.
"These accusations are unsubstantiated and malicious," Iran's mission to the UN told The National, adding that Tehran regards Mr Trump as a criminal for his involvement in the assassination of Suleimani.
"Iran has chosen the legal path to bring him to justice," the mission said.
Mr Trump had a contentious relationship with Iran while in office.
In 2018 he withdrew the US from the Joint Comprehensive Plan of Action, which provided sanctions relief in return for restrictions on Tehran's nuclear programme.
After the US withdrawal, he began a “maximum pressure” campaign of sanctions against Iran.
Adla Massoud contributed to this report from the UN
