LONDON - Former Russian military intelligence colonel Sergei Skripal and his daughter are in a coma after exposure to a suspected nerve agent in the British city of Salisbury.

Skripal, 66, and his 33-year-old daughter Yulia were found unconscious on a bench at a shopping center on Monday. They were believed to have been exposed to a highly toxic chemical, according to Mark Rowley, the Metropolitan Police's counterterrorism chief.

"This is being treated as a major incident involving attempted murder by administration of a nerve agent," Rowley told reporters.

"I can also confirm that we believe the two people originally who became unwell were targeted specifically."

Rowley also said a police officer who treated them is in serious condition.

Malcolm Sperrin, a professor at the Institute of Physics and Engineering in Medicine, said nerve agents could cause heart failure, respiratory arrest, twitching or spasms.

"I'm not aware of a nerve agent having been used in this way previously," he said.

The Russian embassy in the United Kingdom made a statement on Wednesday, saying that Russia still has not received any further information on the incident from Britain, which is "rather worrying".

The statement also said that a recent speech by British Foreign Secretary Boris Johnson is strongly anti-Russian and "looks more like an attempt to send the investigation upon a political track".

Johnson on Monday said Britain "will respond robustly if the attack is found to be the result of hostile activity by another government".

Skripal was sentenced in Russia in 2006 to 13 years in prison for cooperating with the British Secret Intelligence Service MI-6 and releasing names of Russian agents working undercover in Europe.

In 2010, Skripal was pardoned by former Russian president Dmitry Medvedev and then moved to Britain.

Xinhua - Ap - Reuters