Russian authorities say an African student was stabbed to death and another one seriously wounded in two separate incidents in St. Petersburg.

The city's officials say a group of youths attacked the students late Saturday as they were walking to their dormitory from a subway station.

The officials say that, in the first incident, the assailants seriously wounded a student from Kenya but that he managed to escape. He is being treated in a local hospital.

Hours later, on the same street, a young man from Cameroon was found dead with stab wounds, while his friend from Namibia managed to escape unharmed.

Authorities say they have not ruled out any motives for the attack, including extremism and racism. No arrests have been made.