At least 14 people have been killed in a suicide bombing on a trolleybus crowded with morning commuters in Volgograd, less than 24 hours after another deadly suicide attack at the city's main train station.

The authorities initially said 15 people were dead, but a statement from local authorities subsequently put the toll at 14. Dozens were reported injured, including a one-year-old child who was in a critical condition.

The blast ripped apart the trolleybus, leaving a disfigured carcass without the roof and walls.

It is the third bombing attack in Volgograd in three months, with most security experts linking the wave of attacks to the pledge by the Chechen jihadist leader Doku Umarov to disrupt the Olympic Games in Sochi, which start in six weeks' time.

The explosion occurred as the trolleybus approached a stop near a market and the hospital, where many casualties from the train station attack were taken on Sunday. Russian investigators said the explosion was caused by a male suicide bomber.

Local news sites reported that people in Volgograd, a city of more than 1 million inhabitants, were avoiding public transport and walking to work on foot.

"For the second day, we are dying – it's a nightmare," a woman near the scene told the Reuters news agency, her voice trembling as she choked back tears. "What are we supposed to do – just walk now?"

The attacks sent waves of horror across Russia. Popular writer Sergey Minayev said on Twitter the atmosphere reminded him of 1999, when a series of bombing attacks on apartment blocs shook Moscow. "It's like someone has declared a war on us," he wrote.

The death toll from Sunday's attack rose to 17 overnight, with more than 40 injured, some of them still in grave condition. The bomb went off near security gates at the entrance to Volgograd's main train station.

The authorities said it was detonated by a suicide bomber but there were conflicting reports about whether the perpetrator was a man or woman.

The two attacks will raise fears of a concerted campaign of violence before the Olympics, which start on 7 February in Sochi, about 430 miles south-west of Volgograd.

In a video posted on the web in July, Umarov, the leader of insurgents who want to carve an Islamic state out of the north Caucasus, a string of Muslim provinces south of Volgograd, urged militants to use "maximum force" to prevent the games from being held.

Two months ago, another bomb killed 10 people on a bus in Volgograd, which is a few hundred miles from the restive north Caucasus region.

Volgograd, formerly known as Stalingrad, is also of great symbolic importance for Russians as the site of the bloodiest battle of the second world war – something that north Caucausian jihadist websites were quick to emphasise after the train station blast.

Security expert Andrey Soldatov told the Guardian on Sunday the Volgograd tragedy showed that militants from the north Caucasus had sufficient capability and manpower to stage deadly attacks beyond their region. It also means that Russian security bodies will be forced to divert their attention to other regions at a crucial time on the eve of the Olympic Games.