The terrorists who carried out the shooting at the Crocus City Hall concert hall in the Moscow Region have prepared a "window" for escaping to Ukraine, President Vladimir Putin has said during an address to Russians.

He reported the detention of four perpetrators of the terrorist attack, who tried to escape by car towards Ukraine.

According to the Russian president, investigative and law enforcement agencies will do everything to establish all the details of the terrorist attack at Crocus City Hall.

"One unenviable fate awaits terrorists, murderers, subhumans who have no nationality and cannot have one - retribution and oblivion. They have no future," Putin said.

"It is obvious that we are faced with a prepared mass murder of peaceful people," the Russian president said.

According to him, the criminals went about killing in cold blood, shooting Russians at point-blank range, just as the Nazis once acted.

The Russian president noted that additional anti-terrorist and anti-intrusion measures have been introduced in Moscow and other Russian regions.

"Additional anti-terrorist and anti-sabotage measures have been introduced in Moscow and the Moscow region, in all regions of the country. The main thing now is to prevent those behind this bloodbath from committing a new crime," he said.

"We will identify and punish everyone who prepared this strike on Russia... All those involved will be punished. Whoever they are. Whoever directed them. We will identify and punish everyone who was preparing this strike against Russia," the Russian president said.

He also said the authorities were ready to join forces with other countries in the fight against international terrorism. "Our duty is to be together in one line. No one and nothing can shake our cohesion and will," the Russian president said.