Fatina Ubaydatova, police spokeswoman in the restive region of Dagestan, said the convoy hit a bomb on the road south of the regional capital of Makhachkala yesterday evening. The convoy was ferrying federal police forces to the region. Police are sent to Dagestan on a regular basis to supplement local forces.
Later in the day, investigators at the scene found three more explosive devices planted on the side of the road the convoy was travelling on.
Russian state television showed footage of the bombing scene today and said one of the bombs is believed to have contained an equivalent of 5 kilograms of TNT.
But violence subsided significantly as law enforcement agencies clamped down on extremists ahead of the 2014 Winter Olympics in Sochi, and many militants are believed to have left for Syria to fight alongside Islamic State extremists.
Nearly a third of the estimated 3,000 Russians who are believed to have gone to fight in Syria against the government there are from Dagestan.