LONDON (AP) — British police said Monday that a fourth man has been arrested in connection to a series of fires at properties and a car linked to Prime Minister Keir Starmer.

The 48-year-old man, who hasn't been identified, was arrested at Stansted Airport near London on Monday on suspicion of conspiracy to commit arson with intent to endanger life.

No one was injured in the fires that occurred between May 8 and May 12 at a house owned by Starmer, a building where he once lived and a car that he had owned.

Three men have already been charged in connection with the fires: Ukrainians Petro Pochynok, 34, and Roman Lavrynovych, 21, and Ukrainian-born Romanian national Stanislav Carpiuc, 26.

They are being held without bail before a June 6 hearing at London’s Central Criminal Court.

Last week, Kremlin spokesman Dmitry Peskov dismissed a report in the Financial Times that said U.K. security officials were looking into whether Russia was involved in the attacks.

Counterterrorism detectives led the investigation because it involves the prime minister.

Starmer called the fires “an attack on all of us, on democracy and the values that we stand for.”

Starmer and his family had moved out of his north London home after he was elected in July, and they live at the prime minister’s official Downing Street residence.

A Toyota RAV4 that Starmer once owned was set ablaze on May 8, just down the street from the house where he lived before he became prime minister. The door of an apartment building where he once lived was set on fire on May 11, and on May 12 the doorway of his home was charred after being set ablaze.