Croatian Prime Minister Andrej Plenkovic has sent a letter to Austrian Chancellor Sebastian Kurz, extending his condolences to victims' families and support to the Austrian people after a terrorist attack in Vienna, the government said on Wednesday.

Plenkovic stressed that all of Croatia stood by Austria and its citizens after the brutal attack. He said he was deeply confident the people of Vienna, a European and world capital which has always been one of the centres of world science and art, would find the strength and successfully overcome the difficult moments, the government said in a press release.

In the terror attack on Monday night, Kujtim Fejzulai, a 20-year-old Islamic State sympathiser, killed four and wounded more than 20 persons in a shooting in the centre of Vienna before Austrian police killed him.