The South African government has condemned the attacks in Russia in which 31 people died and 104 were injured on Monday.
"We believe that terrorism in any form and from whichever quarter cannot be condoned," international relations department spokesperson Clayson Monyela said.
"The South African government sends it deepest condolences to the government and the people of Russia, particularly the families of the deceased and wish the injured a speedy recovery."
The attacks were in the form of two suicide bombings, and were in the town of Volgograd, 600km from Sochi, which will host the Winter Olympics in February, the Associated Press reported.
Meanwhile, the death toll from the bombings in the southern Russian city of Volgograd has risen to 33 after two victims succumbed to their injuries, the emergency situations ministry said on Tuesday.
"A victim of the explosion at the train station on December 29 died last night in the Volgograd hospital and the number of dead has risen to 18," ministry spokesperson Dmitry Ulanov told the Interfax news agency.
He added that another victim of Monday's suicide bombing on a trolleybus had also died, raising the toll from that blast to 15.
President Vladimir Putin has ordered stepped-up security across the country after the trolleybus bombing at the peak of the morning rush and Sunday's suicide attack, which was blamed on a suspected female suicide bomber.
The attacks have heightened security fears around the Sochi Winter Olympics.
Doku Umarov, the leader of militants seeking to impose an Islamist state throughout North Caucasus, has ordered rebels to target civilians outside the region and disrupt the Games. – AFP, Sapa