Only four days have passed since three people were killed in a knife attack in Nice, France.
The act was described by President Emmanuel Macron as an Islamist terrorist attack.
The French president has now also commented on Monday's suspected terrorist attack in Austria.
"We French people share the shock and grief with the Austrian people who tonight suffered an attack in the heart of its capital Vienna.
After France, another friendly country has now been attacked.
This is our Europe.
Our enemies need to know who they are dealing with.
We will not make any concessions ", he writes on Twitter.
Löfven: We must stand united
Sweden's Prime Minister Stefan Löfven has also condemned what he describes as "terrorist attacks in Vienna".
"My thoughts are with the victims and their families.
We must stand united in the attacks on our open society ", he writes on Twitter.
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