A Russian colonel has been killed in a car explosion outside St Petersburg, according to reports.

Investigators have opened a murder probe after an unnamed serviceman died in the blast in the city’s Pushkinsky District early on Thursday.

A bomb is believed to have been strapped to the underside of the vehicle, detonating on the Kolpino Highway around 7am local time, according to local media.

An unnamed source told Russian outlet Fontanka that a colonel had killed in the blast while driving. A family member travelling with them was injured by shrapnel, they added.

Video shared on Russian Telegram channels showed a large dark-coloured car surrounded by apparent debris and damaged skirting.

The doors and bonnet had been opened as investigators worked on the scene, which was closed off by a police cordon.

The Independent was unable to verify the footage, which appeared across Russian media. News agencies TASS and RIA circulated similar footage of the site.

Nobody has taken responsibility for the explosion, which comes amid Russia’s nearly five-year war in Ukraine.

Another serviceman was killed in a car explosion in the same district of Russia’s second largest city on August 27.

Other car bombs attacks have occurred in Moscow and Crimea , which Russia annexed from Ukraine in 2014, in recent months.

Russia earlier this year accused Ukrainian intelligence of being behind an assassination attempt on a Russian general in Moscow. Ukraine denied any involvement.

Ukraine was also accused of carrying out a car bombing in Moscow that killed Russian Lt Gen Fanil Sarvarov last year. Kyiv did not take responsibility for that attack, either.

The veteran officer of the armed forces had been responsible for the military’s combat training and readiness for the war in Ukraine before his death.

Russia has not officially confirmed the rank of the serviceman killed on Thursday and investigators are still working to establish the exact cause.

“Investigators and forensic experts, together with operational officers, are currently examining the crime scene, and a number of necessary forensic examinations are being ordered,” the Investigative Directorate said on Telegram.

“All the circumstances of the incident are being clarified.”

Russia’s FSB separately said that it had arrested four alleged Ukrainian intelligence agents, including a foreign national, accused of gathering information on participants in [the war].

The suspects were accused of spying on Russia’s “defense industry enterprises and energy facilities, with the aim of committing acts of terrorism and sabotage”, the FSB claimed.