(AFP) - "Suspected of having committed acts of espionage, Martin Ryan, a French national, was arrested on 4 December 2023," said Azerbaijan's ambassador Leyla Abdullayeva.
She said judicial authorities had ordered him to be detained "for four months".
The French embassy in Baku was notified as soon as he was arrested, she added.
'Arbitrary detention'
The French foreign ministry confirmed that a French national was being held in Azerbaijan.
"We consider this detention to be arbitrary, and ask for our fellow national to be freed without delay," the ministry said.
Ryan's father Richard said the family had spoken to him.
"We spoke to him four times, each time for two minutes," he told French news agency AFP. "He says he's being treated well and is getting on well with his lawyer."
According to his father, Ryan believes his detention is linked to the tensions between the two countries.
"Once he told me: 'They wanted to use me as a pawn'," Richard Ryan said.
On Tuesday, the Frenchman's court-appointed lawyer, Nizami Aliyev, told AFP that Ryan could face up to 15 years in prison if convicted.
He said he could not share any information and stressed it was "risky to talk about the case."
Aliyev also claimed that Ryan had been in contact with French people who he later learned were "agents" of French intelligence.
"Martin is not an agent, he is a citizen," the lawyer said.
Tensions between France and Azerbaijan
Diplomatic tensions between Paris and Baku escalated at the end of December when Azerbaijan ordered two French diplomats to leave the country.
France declared two Azerbaijani diplomats "persona non grata" as a reciprocal measure.
In November, Azerbaijani President Ilham Aliyev accused France of inciting conflict in the Caucasus by arming Armenia.
Azerbaijan and Armenia have in the last three decades fought three wars over the Azerbaijani region of Nagorno-Karabakh, which was seized by Armenian forces when the Soviet Union fell apart.
In the latest war, Azerbaijan took total control of Karabakh in a surprise offensive last year.
The move sparked some international condemnation, including from France, but also hope of a settlement to end years of conflict between Baku and Yerevan.
In November last year, Paris had also linked Azerbaijani figures to a disinformation campaign aimed at tarnishing France's reputation as host of the 2024 Olympic Games.