A 20-year-old British man has been charged with masterminding an arson plot against a Ukrainian-linked target in London for Russia and Moscow's ambassador was summoned by the government, authorities said Friday.

"Included in the alleged activity was involvement in the planning of an arson attack on a Ukrainian-linked commercial property in March 2024," said a Crown Prosecution Service statement.

The government said it summoned the Russian ambassador Andrey Kelin "following allegations of Russian orchestrated malign activity on UK soil".

Kelin dismissed the claims of a link to Russia as "absurd" and "unfounded", according to a statement sent to the state-run TASS news agency.

Court documents allege that Dylan Earl, from Leicestershire in central England, was connected to Russia's Wagner Group, which Britain has put on its list of "terrorist" groups, the Press Association news agency reported.

He is accused of organizing and paying for an arson attack on two units at an industrial estate in Leyton, east London, on March 20, which required 60 firefighters to bring under control.

The alleged target is referred to as "Mr X" in the charges.

The CPS, which brings prosecutions in England and Wales, said two other men -- Paul English, 60, and Nii Mensah, 21 -- had also been charged with aggravated arson in connection with the case.

Two other suspects were named. Jake Reeves, 22, was charged with agreeing to accept a material benefit from a foreign intelligence service as well as aggravated arson.

Dmitrijus Paulauska, 22, has been charged with having information about terrorist acts, the CPS added.

  'Deeply concerned' 

 UK Foreign Secretary David Cameron said: "While we must let the judicial process run its course, I am deeply concerned by allegations of British nationals carrying out criminal activity on UK soil to benefit the Russian state."

"We will use the full weight of the criminal justice system to hold anyone found guilty of crimes linked to foreign interference to account," he wrote on X, the former Twitter.

Cameron's ministry demanded "an immediate cessation of this activity", adding it would "continue to work with our allies to deter and defend against the full spectrum of threats that emanate from Russia."

In Berlin, NATO chief Jens Stoltenberg said that "unacceptable" Russian-backed plots would not deter the alliance from supporting Ukraine.

Investigators last week arrested two German-Russian men on suspicion of spying for Russia and planning attacks in Germany, including on US army targets, to undermine military support for Ukraine.

Russian officials rejected the claims.

"Such acts are dangerous and unacceptable," Stoltenberg told a news conference.

"They will not deter us from providing support to Ukraine and we are coordinating closely in our response to any hostile act against NATO allies," he said.

Dominic Murphy, head of London's Metropolitan Police Counter Terrorism Command, which is leading the investigation, said: "This is a highly significant moment and investigation for us."

"Not only are the charges that have been authorized by the CPS extremely serious, but it is also the first time that we have arrested, and now charged anyone using the powers and legislation brought in under the National Security Act."

The National Security Act 2023 was designed to respond to "the threat of hostile activity from states targeting the UK's democracy, economy, and values", the government said.

All five suspects are to appear at the Central Criminal Court in London on May 10.