Tillerson says ex-spy's poisoning in UK 'will trigger a response'

US Secretary of State Rex Tillerson has stated that the poisoning of ex-spy Sergei Skripal in Britain "clearly came from Russia" and "certainly will trigger a response."

However, he said that he would not dwell upon what response might follow, according to a media report.

Tillerson spoke to reporters on his aircraft as he flew from Nigeria to Washington.

Retired military intelligence officer Skripal, 66, and his daughter, Yulia, 33, were found slumped on a bench in Salisbury city centre on March 4. However, they remain in a critical but stable condition in hospital.

The White House noted that the use of a highly lethal nerve agent against Skripal and his daughter "is an outrage."

Spokeswoman Sarah Huckabee Sanders on Monday underscored that Washington has been keeping a tab on the incident in England very closely, adding that the attack was "reckless, indiscriminate and irresponsible."

According to the reports, Skripal was convicted by the Russian government of passing secrets to UK's Secret Intelligence Service MI6 in 2004, but was given refuge in the UK in 2010 as part of a "spy swap.