Argentina's military and federal police scrambled to deal with a bomb threat made against the presidential palace in Buenos Aires while President Mauricio Macri was there on Monday, just hours after a man was arrested trying to enter the building with a gun, an official with the presidential press team said.

The threat against Casa Rosada was made via a phone call in which a person indicated a plan to put a bomb inside a car, the office of Argentina's Secretary General confirmed to Reuters.

The military activated its protocol for such threats, and a team was dispatched to check and secure the entrances of Casa Rosada, the presidential palace and seat of the national government. No car containing explosives was found, and the building was not evacuated.

"There is no possibility of a bomb entering without detecting it," an official from the office of the secretary general said.

Local media reported that another threat was made against a congressional office and a response team was also on the scene there.

The bomb threat followed the arrest of a man carrying a gun who claimed to have a meeting with Macri, his office said in a separate statement. The city has faced false bomb threats before, including ahead of a meeting of the Group of 20 nations there last year.

Security personnel said Francisco Ariel Muniz, 36, had tried to enter the building with a .44 Magnum Taurus revolver inside his briefcase and told officials he was there for an appointment with center-right leader Macri.

After officials confirmed that no such meeting was scheduled, he tried to leave the briefcase behind. The statement said Muniz was detained by security personnel. Security Minister Patricia Bullrich tweeted that the gun was not loaded.

Macri, who came into office in 2015, will seek re-election in October in what is likely to be a closely fought battle. He has been falling in opinion polls amid high inflation and a tumbling peso that has hurt voters in the recession-hit nation.

An attack outside Argentina's Congress last week led to the deaths of a senior lawmaker and an aide, though local officials and media have indicated the motive behind the "mafia-style" shooting was personal rather than political.