Moscow is facing a "global wave of revulsion" in response to the nerve agent attack on a former Russian spy, Britain's Foreign Secretary Boris Johnson said.
His intervention came after British counter-terror police on Wednesday said Sergei Skripal and his daughter first came into contact with a nerve agent at their home address in Britain -- with the highest concentration on the front door.
The March 4 attack on the Skripals in the English city of Salisbury has been met with a major response that has seen more than 150 Russian diplomats expelled from countries around the world.
British authorities have blamed Moscow, which denies any involvement, and said a Soviet-designed nerve agent dubbed Novichok was used in the poisoning.
"The Kremlin underestimated the strength of global feeling," Johnson said at a speech late Wednesday in London.
"We believe the Skripals first came into contact with the nerve agent from their front door," said Dean Haydon, Britain's counter-terror police chief.
The BBC's security correspondent Gordon Corera said the highest concentration was found on the Skripals' door handle and could have been administered through a "gloopy substance which could have been smeared on".
The Skripals remain in a coma in hospital, while a police officer who responded to the attack was discharged last week.
His 33-year-old daughter Yulia Skripal is "improving rapidly and is no longer in a critical condition. Her condition is now stable", said the hospital treating the pair since the March 4 attack.
Skripal sold secrets to Britain and moved there in a 2010 spy swap. His daughter was visiting from Russia.