The U.S. Federal Bureau of Investigation (FBI) "is investigating what appears to be an attempted assassination" of former U.S. President and current Republican presidential candidate Donald Trump, the agency said on Sunday, just two months after an attempt on his life at a Pennsylvania rally.

Trump was safe after shots were fired at Trump International Golf Club in South Florida on Sunday. A Secret Service agent, who was ahead of the former president, spotted a rifle barrel sticking out of a fence and "engaged" with the suspect. Trump was moving between holes five and six at his golf course with donor Steve Witkoff when gunshots were heard. The course was immediately locked down.

Martin County Sheriff William D. Snyder said at a press conference later in the day that his agency "flooded" Interstate 95 and closed a large swath of the highway before eventually safely stopping the suspect's vehicle and detaining him.

The suspect was not armed when law enforcement officials took him out of the car. He has not made any statement so far.

After the incident, Trump said in a fundraising email that he is "safe and well," adding that "my resolve is only stronger after another attempt on my life! ... I will never slow down. I will never give up. I WILL NEVER SURRENDER!"

Trump's running mate, J.D. Vance, said he spoke with Trump after the security incident. "I'm glad President Trump is safe. I spoke to him before the news was public and he was, amazingly, in good spirits," Vance wrote on X.

President Joe Biden and Vice President Kamala Harris were both "relieved to know" that Trump was safe and had been briefed on the security incident.

In her statement posted on X Sunday, Harris said, "I have been briefed on reports of gunshots fired near former President Trump and his property in Florida, and I am glad he is safe. Violence has no place in America."

Senate Majority Leader Chuck Schumer said he had been briefed by acting Secret Service Director Ronald L. Rowe Jr. over the incident.

"I applaud the Secret Service for their quick response to ensure former President Trump's safety," Schumer said. "There is no place in this country for political violence of any kind. The perpetrator must be prosecuted to the fullest extent of the law."

Meanwhile, the leaders of the bipartisan task force in the U.S. Congress that has been investigating the earlier assassination attempt on Trump said they are monitoring the situation and have requested a briefing from the Secret Service.

Golf courses, and in particular Trump's properties, have long been a source of concern among Secret Service officials tasked with securing the grounds while he plays, CNN quoted people familiar with the matter as saying.

"A golf course is often the largest outdoor area a president can visit, and their design – often abutting public roads and containing elements like trees and hills that can conceal would-be assassins – make them particularly difficult for the agency to secure," the report said.

The incident raises new questions about how to keep Trump safe – not only while he is campaigning across the country, but while he spends time at his own clubs and properties, said the AP news agency.

"Unlike typical VIPs, who live in private residences with tall fences, Trump, while in Florida, resides in a club open to dues-paying members and often spends his downtime at his golf courses," it said.

Trump was the target of an assassination attempt during a July rally in Butler, Pennsylvania, when a staccato of shots rang out in the middle of his speech, killing one attendee and severely injuring two others. According to the FBI, either a bullet or a bullet fragment struck Trump, wounding him in the ear.