By Carlo Muñoz - 12/29/13 05:29 PM EST
The Obama administration harshly denounced the actions of those responsible for Sunday's deadly suicide bombing in southern Russia, vowing to stand alongside Moscow in its counterterrorism efforts.
"The United States condemns in the strongest terms today's terrorist attack in Volgograd," State Department spokeswoman Jen Psaki said in a statement late Sunday.
"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.
Russian authorities are still investigating the attack, while no group has yet claimed responsibility for the strike.
A second bombing, on a Volgograd bus, killed at least 14 people on Monday, according to multiple reports.
"That confirms the investigators' version that the two terror attacks were linked," Markin said in a statement. "They could have been prepared in one place."
A female suicide bomber detonated her deadly ordnance aboard a bus in the city in October, killing six and injuring over 30 in the attack.
On Friday, a car bomb went off in the nearby city of Pyatigorsk, killing three bystanders in the blast.
The area in southern Russia where the attacks took place, along the border of the contentious North Caucus region, has long been a hotbed for Islamic fundamentalist groups.
Fighters from the area have reportedly made their way to battlefields in Syria and Afghanistan.
Dzhokhar Tsarnaev, one of the two brothers responsible for the Boston Marathon bombings earlier this year, allegedly made contact with militant Islamic groups while visiting the Northern Caucus area of Dagestan.
The attacks come as Russia is preparing to host the 2014 Olympic Winter Games in Sochi.
--This report was updated at 6:24 a.m. on Monday.