French detectives are investigating whether a group of heavily armed gunmen who attacked a convoy of vehicles carrying a Saudi prince and his entourage in the north of Paris wanted money or important diplomatic documents.

The attackers, who police said were clearly well informed, struck on Sunday evening on the Champs Elysées, after the motorcade of a dozen vehicles had left the luxurious George V hotel and headed to Le Bourget airport, nine miles (15km) north of the French capital.

As the convoy arrived at Porte de la Chapelle, which leads to the péripherique ring road, the attackers – who were travelling in two BMWs without number plates – forced the Saudis' cars to stop, and went straight to one of the vehicles, a Mercedes people carrier.

The robbers, said to number between five and eight, seized the Mercedes and its three occupants – as well as €250,000 and what Le Parisien newspaper described as sensitive documents.

Soon afterwards the robbers released the hostages and abandoned the vehicle, which was found an hour later in Saint-Mesmes, a village in the Ile-de-France region north-east of Paris, along with one of the BMWs. Both vehicles were burnt out.

Some reports suggested the robbers were carrying handguns, others that they were armed with Kalashnikovs, but detectives said no shots were fired and no one in the convoy was hurt. Two €500 notes, documents in Arabic and some medical drugs were said to have been found near the wreckage.

Rocco Contento, of the SGP police union, said the documents came from the Saudi embassy in Paris. "It was clearly an ambush by a commando group that was well-informed, particularly of the time the vehicles would be passing," he told French television.

Romain Nadal, spokesperson for the French foreign ministry, called the attack unacceptable. Police have not named the Saudi prince involved, and the Saudi embassy has declined to comment.

Nicolas Comte, secretary general of the main police union, Unité-SGP, described the attack as strange and unusual. He told AFP: "We have to establish whether it was the money or documents that were targeted. We also have to hope that the Saudi authorities will cooperate with the investigation."

One detective added: "If they were seeking sensitive information, the nature of the robbery changes. We're no longer faced with organised bandits, but something more complicated."

He said the first elements of the inquiry suggested the robbers were "quite expert … and aware of what they would find by attacking this one vehicle [the Mercedes] and not the others".

The George V hotel from which the convoy departed is owned by Prince Al-Waleed bin Talal bin Abdulaziz al Saud, a nephew of King Abdullah. It is not known whether he was in the convoy.

He was listed as among the 100 most influential people in the world by Time magazine in 2008. He is founder and 95% owner of Kingdom Holding Company, which has investments in banking, financial services and hotels, media, aviation and property.

He is also Citigroup's largest individual shareholder and the second largest voting shareholder in News Corporation. Last year he was listed as the 26th richest man in the world by Forbes magazine, with an estimated $26bn fortune.

• This article was amended on 19 and 20 August 2014 to clarify the position of the Hotel George V and the motorcade.