Spokeswoman Jane Crawford said in an email that the company was making "steady progress" and that some systems were coming back online.

The company, which runs some 400 healthcare centers and hospitals across the United States and the U.K., has been struggling to restore its systems since the incident began on Sunday.

The firm has said its U.K. operations are unaffected.

(Reporting by Raphael Satter, Editing by Franklin Paul)