WASHINGTON, Dec. 29 -- The United States on Sunday denounced a deadly attack in the Russian city of Volgograd, calling it an act of terrorism.

"The United States condemns in the strongest terms today's terrorist attack in Volgograd," State Department spokeswoman Jennifer Psaki said in a brief statement.

"We send our sincere condolences to the families of the victims and stand in solidarity with the Russian people against terrorism of any kind," she added.

At least 16 people were killed and dozens of others injured when a female suicide bomber blew herself up at a railway station in Volgograd, a city near the volatile North Caucasus region.

The attack was the second of its kind that had rocked Volgograd recently. Two months ago, a female suicide attacker blew herself up on a bus, killing seven and injuring dozens of others.

Russian President Vladimir Putin warned in September that the situation in the North Caucasus remained a challenge for state security. He called on all law enforcement departments to be mobilized to maintain law, order and peace in the region.