"Later this week we will be announcing new actions on ransomware followed next week by further announcements on steps we are taking to improve our cyber resilience here in the United States", Sullivan said during a conference organised by the National Security Committee on Artificial Intelligence.
The statement comes amid reports that all the websites associated with the cybercriminal group REvil are down.
Last week, the White House said the United States would take action against REvil in response to the ransomware attack against the IT management software company Kaseya, which affected a number of US companies.
The gang, which was also blamed for the May hacking of the meat processing giant JBS, is reportedly linked to Russia, although Moscow denies it.