Johnson defended the measures announced on Wednesday and suggested that there could be further consequences for wealthy Russians with assets in Britain.
"We will go after the money and actually we are going after the money," he said, adding that the National Crime Agency and Economic Crimes Unit were investigating a wide range of individuals. He declined to give details, citing legal reasons.
"What people want to see is some of the very rich people ... whose wealth can be attributed to their relationship with Vladimir Putin, it may be that the law agencies, that the police will be able to put unexplained wealth orders on them, to bring them to justice for their acts of gross corruption," he said.
Johnson also said he had been heartened by strong expressions of support from the United States and other allies -- although it remains unclear whether there will be a coordinated international response to the Novichok attack.
France, which on Wednesday had said it wanted proof of Russian involvement before deciding whether to take action against Russia, appeared to change its position on Thursday, saying it agreed with the assessment of its NATO ally Britain.
"France agrees with the United Kingdom that there is no other plausible explanation (than Russian involvement) and reiterates its solidarity with its ally," President Emmanuel Macron's office said.