BEIJING -- Chinese President Xi Jinping extended condolences to his Russian counterpart Vladimir Putin on Monday over two terror attacks in Russia's southern city of Volgograd, which left dozens of people dead.

In his message, Xi expressed his sympathy and condolences for the heavy casualties caused by the two explosions.

On the same day, Chinese Premier Li Keqiang also sent a message to Russian Prime Minister Dmitry Medvedev over the deadly attacks.

At least 15 people were killed and 27 others injured when a suspected bomb exploded on a trolley bus in Volgograd on Monday and a suicide bomber attacked a railway station in the same city Sunday, killing 17 and injuring 45.

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Second blast kills 14 in Russian city

Suicide bomber kills at least 16 at Russian train station

A suicide bomber set off a blast in the entrance hall of a Russian train station on Sunday, investigators said, killing at least 16 people in the second deadly attack within three days as the country prepares to host the Winter Olympics.

Authorities said the attacker detonated a shrapnel-filled bomb in front of a metal detector just inside the main entrance of the station in Volgograd, a busy hub north of the violence-plagued North Caucasus region on Russia's southern fringe.