According to Austrian police, shots were fired Monday evening in central Vienna.
At least one victim is to be deplored and one of the attackers was also shot dead.
Another would be "on the run", according to the Interior Ministry.
Several injured have been identified.
"Our enemies must know who they are dealing with. We will not give in," President Emmanuel Macron commented on Monday evening after the announcement of the fatal shooting in the center of Vienna.
"We, the French, share the shock and the pain of the Austrian people (...). After France, a friendly country is being attacked. It is our Europe. Our enemies must know who they are dealing with. We will not give up anything ", tweeted the head of state in French and then in German.
The Elysee Palace specified that Emmanuel Macron had spoken in the evening with Austrian Chancellor Sebastian Kurz, to whom he "expressed his total solidarity, his support and offered France's help if necessary."
"We are and will always be united against barbarism and obscurantism"
Former President François Hollande for his part brought his "unwavering support to the Austrian people and the Jewish community of Vienna, targeted by this appalling anti-Semitic attack. We are and will always be united against barbarism and obscurantism", a- he reacted on the social network Twitter.
The mayor of Paris, Anne Hidalgo expressed in a tweet her "support for the Jewish community, Viennese and Viennese and its Mayor, Michael Ludwig, after the attack in front of a synagogue in Vienna".
"Paris is at your side," she said.
"Irrepressible fraternity with the Jews of Austria and the victims of the heinous attack in #Vienne," tweeted for his part the leader of the Insousmsis, Jean-Luc Mélenchon.
"We French, knowingly feel the shock. The Austrians can count on us," he added.
The shooting in the center of the Austrian capital left two dead: a passer-by and a woman who died of her injuries.
One of the attackers was shot and "at least one suspect" is on the run, authorities said.
Six different places were targeted, according to the same source, and several people were injured.