LONDON — The former Russian spy Sergei V. Skripal and his daughter, Yulia Skripal, remain unconscious and are in critical but stable condition, Britain’s home secretary, Amber Rudd, told lawmakers on Thursday, adding that it was too early to apportion blame for a “brazen and reckless” attack involving a nerve agent.

A police officer who assisted the two victims, and was also hospitalized, is in serious but stable condition and is “conscious, talking and engaging,” Ms. Rudd added, in an update on an investigation that has stirred much speculation about Russian involvement. In a police statement, the officer was identified as Nick Bailey, a detective sergeant.

While she described the incident as an “attempted murder in the most cruel and public way,” Ms. Rudd said she would refrain from attributing blame until the hundreds of antiterrorism police and security officials working the case reached conclusions based on solid evidence.

“There will come a time for attribution,” Ms. Rudd said, promising that there would be “consequences” for those behind the attempt on the life of Mr. Skripal and his daughter, who were taken ill on Sunday afternoon in the city of Salisbury.