The diplomat said the explosions, which took place during rush hour and killed several people, were 500 meters, as the crow flies, from the Estonian embassy. It is not yet clear if they were missiles or carried out by drones.

Russia did not attack critical infrastructure in the capital, he said.

"There are problems with the electricity supply and with water. But I believe that the Ukrainians will get the power lines or substations repaired within hours," Kuusk told ERR earlier on Monday.

He thought it likely more attacks could follow.

The reasons behind the attack were both Saturday's explosions on the Kerch Bridge, which links the occupied Crimean peninsular with the Russian mainland, and Russia's weak performance on the battlefield, he reasoned.

"The initiative on the battlefield had been in the hands of the Ukrainians since mid-August already. The bombing of civilian targets and peaceful residents shows that they would like to regain the initiative somehow," said Kuusk.

Asked if Russia could threaten — again — to use a nuclear bomb, Kuusk said it is possible.

"At the moment, there are plans for the annual autumn strategic nuclear weapons exercise, which has not taken place yet. I would not be surprised if it happened within a few days," he said.

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