A bomb has exploded at a bus stop in the south Russian city of Voronezh, injuring at least one person in the third such attack there since February.
One theory for the attacks is that they are the work of gangsters
The bomb, thought to have been a home-made device, went off in the morning at a junction in the north of the city, police told Russian news agencies.
A similar attack left one dead and seven injured on 19 July while an attack on 19 February injured two.
The attacks remain unsolved with police keeping an open mind as to motive.
Monday's blast blew out windows in passing cars and was so loud it could be heard in the centre of Voronezh, 475km (300 miles) south of the capital, Moscow.
Reports said that up to two people were injured, one of them a woman.
Police have been investigating various theories for the attacks, ranging from vandalism to terrorism.
Voronezh has a population of more than 800,000 and has a large community of foreign students, many of them on Russian-language induction courses.