Three people were killed and 21 others injured when an explosion went off close to a restaurant terrace on Kudrinskaya Square in Moscow on Saturday evening, according to Russian officials.

Russia's Interior Ministry confirmed the death toll and said the blast occurred at about 8.10pm local time, which was 6.10pm in the UK. The explosion happened near an upscale Italian restaurant in one of Moscow's seven Stalin-era skyscrapers, and the square was quickly cordoned off by the emergency services.

Some of the wounded were taken to hospital, and reports said a number of the injured were fighting for their lives. Some of those injured were described as being in a serious condition. The restaurant was reported to have been busy at the time, although officials gave no immediate details about how many people were on the terrace when the blast happened.

The cause of the explosion was not immediately established. Russian state television suggested that a gas canister may have detonated, while other unconfirmed reports said a homemade explosive device had been used. No official confirmation was given for either explanation, and an investigation was under way at the scene. An official inquiry was opened to establish how the blast was caused.

The building that houses the restaurant is one of the high-rise towers built in Moscow during the Stalin era and is among the most recognisable structures in the Russian capital. The towers in this group are often referred to collectively as the Seven Sisters, and the block on Kudrinskaya Square is one of the most visible of them. The blast occurred beside the restaurant's terrace, in an area facing the square, on a Saturday evening when outdoor dining spaces in the city would normally be busy.

Officials did not release the identities of the three people killed or provide a breakdown of the 21 injuries. The exact position of the explosion had not been confirmed, and there was no immediate word on whether all of the wounded had been accounted for. Early reports had suggested that more than a dozen people had been injured before the ministry confirmed the higher figure.

Police kept the public away from Kudrinskaya Square while investigators examined the scene. The authorities have not said whether the blast is being treated as an accident or as a deliberate act. No further statement was released in the hours after the explosion, and the area remained closed while the emergency response continued. No timetable was given for when the cordon would be lifted.