A British man has been killed and his stepson wounded after being shot during a suspected robbery outside a five-star hotel in Buenos Aires, officials say.
The victims are believed to be Matthew Gibbard, 50, a businessman from Northamptonshire, and Stefan Zone, 28.
They were taken to hospital after the attack in the Puerto Madero area of the Argentine capital.
Four people have been arrested after police investigating the crime carried out 18 raids, local officials said.
The Foreign Office said it was supporting the family of two British men after an incident in Buenos Aires.
Security camera footage shows the two men getting out of a white van outside the Faena Art Hotel in Puerto Madero, an exclusive waterfront district popular with tourists.
At about 11:00 local time (14:00 GMT) on Saturday, they were approached by at least two men on a motorbike, apparently accompanied by another vehicle.
The images show the two British nationals resisting the attempt to steal their baggage, and a fight goes on for some 40 seconds. The suspects left the scene and police are still searching for them.
Police are trying to establish whether the men were victims of a random attack or followed by the robbers from the airport, Clarín newspaper reports (in Spanish). According to the newspaper, the 50-year-old's mother and wife as well as the 28-year-old's wife and his brother were with them.
A Foreign Office spokeswoman said: "We are supporting the family of two British men following an incident in Buenos Aires, and are in contact with the local authorities there."
Argentina's newly elected president, Alberto Fernandez, who lives near the hotel in Puerto Madero, has responded to the robbery.
"We must be tough," he said. "We can't put up with this. We need to find the people responsible for this and make them pay with the full force of the law."
"It was an atrocious incident, like many that happen in Argentina, because criminality hasn't gone down, despite what the official figures say.
"I urge everyone to stand up to it and be uncompromising when facing crime."
Attacks by robbers on motorbikes, known as motochorros, are not uncommon in Buenos Aires. The city is generally safe, but other foreigners have been targeted in the past.
Travel expert Simon Calder told the BBC that crime in parts of Latin America is "opportunist".
"This is an awful tragedy," he said. "I'm afraid crime, particularly aimed at well-to-do tourists, is all too common, not just in Buenos Aires but in the big South American cities.
"Argentina is a superb a destination, very safe, and a welcoming country.
"Unfortunately, like elsewhere in Latin America, there are criminals who will use violence if they need too.
"My advice is to run away if you can or hand over what they want."
More than 111,000 British nationals visited Argentina in 2018, according to the Foreign Office, which said most visits are "trouble-free".
Tourists are warned to be alert to street crime, including armed robberies, and advised to hand over cash and valuables without resistance.