Two bomb blasts rocked a rush-hour commuter train (search) carrying college students in southern Russia on Wednesday, killing at least four people and wounding dozens.

The bombs were planted on the tracks linking Kislovodsk to Mineralnye Vody in the Caucasus region. There were about 50 people in the third car of the six-car train, which was directly hit by one blast, Railway Ministry spokesman Konstantin Pashkov said.

Survivors reported many of the passengers were college students. Many Russian universities began their fall semesters this week.

There were varying reports on the casualty toll.

Dmitry Oliferenko, a spokesman for President Vladimir Putin's (search) envoy to southern Russia, said five people were killed, while Russian Railways Minister Gennady Fadeyev said in televised comments that six died.

However, Regional Emergency Situations Ministry spokesman Igor Mikhailov said four were killed and 33 were wounded in the explosions as the train was approaching a station in Podkumok, a town on the outskirts of Kislovodsk, 870 miles south of Moscow.

Mikhailov said 21 of the injured remained hospitalized, eight of them in serious condition.

NTV television reported that the dead were an 18-year-old woman, two 21-year-old men and a 15-year-old boy.

No group immediately claimed responsibility for the blasts.

Viktor Kazantsev, President Vladimir Putin's envoy to southern Russia, told state television that police had arrested a man suspected of detonating the bombs. Police said the suspect was injured in the explosion and was hospitalized in serious condition.

Russia has been hit recently by numerous bombings and other attacks, which the government usually blames on rebels from Chechnya (search).

An officer at the headquarters of the Caucasus Military District, which oversees Chechnya, said on condition of anonymity that the military had received intelligence information that the rebels were preparing a series of attacks in southern Russia.

Wednesday's explosions occurred just as Putin was scheduled to chair a meeting of regional governors in Rostov-on-Don, about 280 miles northwest of the site of the bombings. Putin spoke with Stavropol governor Alexander Chernogorov about the blasts, news agencies reported.