British authorities have identified a third agent involved in the attack against former Russian spy Sergei Skripal, The Telegraph reported.

The UK earlier this month accused two Russian intelligence agents of the attempted assassination.

The third agent was also part of Russia's intelligence service, and this person visited England to check out the layout of Skripal's neighborhood before his colleagues arrived, The Telegraph said.

The report comes as the investigative-journalism site Bellingcat identified one of the suspects as Col. Anatoliy Chepiga, a highly decorated officer with the GRU, Russia's intelligence service.

The Kremlin has repeatedly denied knowledge of the attack. The latest findings may weakening this claim.

A third Russian intelligence agent went to England to plan the nerve agent poisoning of a former Russian spy earlier this year, The Telegraph has reported, casting further doubt on the Kremlin's claims that it had no knowledge of the attack.

The UK in early September accused two Russian men, who traveled under the names Alexander Petrov and Ruslan Boshirov, of the attempted assassination.

British officials say they were members of the GRU, Russia's intelligence service. President Vladimir Putin claimed the two men were civilians, and the two men even appeared on Russian TV to say they were visiting Salisbury as tourists.

Surveillance camera footage of Alexander Petrov and Ruslan Boshirov, the two suspects in the Skripal attack, at Salisbury train station the day before Skripal's collapse. London Metropolitan Police

UK counter terrorism police and the security services identified the third agent, and say the person visited Salisbury to prepare for the attack on Sergei Skripal before two of his colleagues arrived, The Telegraph reported on Thursday night.

Authorities believe the third agent visited Salisbury ahead of the attack, and reported the layout of Skripal's neighborhood and property to the two agents who later carried out the attack, the newspaper said.

A composite photo of Sergei and Yulia Skripal. AP/Facebook

Skripal and his daughter Yulia collapsed this March after being exposed to novichok, a military-grade nerve agent, which was smeared on his front door.

A British couple who lived nearby were also exposed to the same batch of nerve agent in July, which led to the death of one woman.

The investigative-journalism site Bellingcat this week identified Boshirov as Col. Anatoliy Chepiga, a highly decorated officer with the GRU, Russia's intelligence service.

Photographs showing Alexander Petrov and Ruslan Boshirov, two men accused of poisoning former spy Sergei Skripal. Boshirov was identified as Russian intelligence officer Col. Anatoliy Chepiga this week. London Metropolitan Police

Bellingcat's findings suggest that Putin was in fact aware of the suspect's legal identity, which would seem to disprove the Russian president's claim that he didn't know who Boshirov and Petrov were, that they were civilians, and that the Kremlin had no knowledge of the Skripal attack.

The findings are also in line with the British government's claim, citing security and intelligence agencies' investigations, that Boshirov and Petrov were officers from Russia's intelligence services.

Prime Minister Theresa May earlier this month also said that authorization for the attack "almost certainly" came from senior members of the Russian government.

A composite photo of Russian President Vladimir Putin and British Prime Minister Theresa May. Reuters/AP

The Skripal poisoning caused a large diplomatic rift between the UK and Russia. London accused Moscow of being behind the attack, which the Kremlin repeatedly denied. More than 20 countries also joined the UK in expelling Russian diplomats as punishment.

The British Foreign Secretary, Jeremy Hunt, on Thursday suggested that Russia was not expecting such a large international response to the attempted assassination.

Hunt told Sky News on Thursday:

"They can't have been expecting Theresa May to put together a coalition that saw 153 Russian spies expelled from capitals in 28 countries across the world.

"So they paid a very high diplomatic price — but they need to understand that it will not be a comfortable place for Russia in the world if this is the way they behave."

Business Insider has contacted the Russian Embassy in the UK for comment.

The London Metropolitan Police, who is leading the investigation into the attack, declined to comment on The Telegraph's report.

The force told Business Insider in a statement on Thursday that international arrest warrants for Petrov and Boshirov remain active. However, Russia does not extradite its own citizens.