BERLIN -- An Afghan man has been detained in connection with knife attacks in Vienna in which four people were severely injured, Austrian police said Thursday.

The 23-year-old was detained shortly after the stabbing of a 20-year-old man, also from Afghanistan, on Wednesday night, police spokesman Patrick Maierhofer told The Associated Press.

Maierhofer said police are still investigating whether the suspect is also responsible for the stabbing of an Austrian family about an hour earlier, also in the heart of Vienna.

All three family members, the 67-year-old father, the 56-year-old mother and their 17-year-old daughter, as well as the 20-year-old Afghan victim suffered life-threatening injuries and were taken to the hospital. The names of the victims were not given.

Maierhofer said the attack did not appear to be terror-related, but it was too early to say anything about the motive of the attacker.

"We are still investigating and cannot say what motivated him," Maierhofer said. "We cannot even say, at this point, if the detained suspect attacked all four persons or if a second suspect was involved who is still on the run."

Local Austrian media reported Thursday that police had increased their presence in Vienna's downtown area.