Two bombings at a train station and on a trolleybus killed at least 26 people within 24 hours in the southern city of Volgograd

Two bombings at a train station and on a trolleybus killed at least 26 people within 24 hours in the southern city of Volgograd, investigators said.

An explosion killed at least 10 people and injured 15 in the trolleybus during rush hour after 8:10 a.m. local time, according to the country’s Investigative Committee. A suicide bomber killed at least 16 people in an attack yesterday at about 1 p.m. in front of a metal detector placed at the entrance to the train station in Volgograd, the law-enforcement agency said on its website. More than 35 people remain hospitalized after the first blast.

The attacks come as Russia prepares to host the Olympics in February in Sochi, a Black Sea resort close to areas of unrest in the North Caucasus region. Volgograd is about 700 kilometers (435 miles) north-east of Sochi.

President Vladimir Putin’s government had planned to beef up security starting on Jan. 7, according to the state-run news service RIA Novosti.

The Investigative Committee is treating both bombings as terrorist attacks. An explosive device may have been planted in the vehicle, Interfax reported, citing the National Anti-Terrorist Committee.