British authorities are investigating two plots involving mostly Iranian nationals in the United Kingdom that appear at this stage of the investigation likely to be state-sponsored, according to a senior official briefed on the threat. 

Eight people have been arrested in London and in other parts of the U.K. over the weekend, according to statements from local authorities. Seven of them are Iranian nationals, officials said.

Police said three of the men were arrested under Section 27 of the U.K.’s 2023 National Security Act, which allows police to arrest people suspected of acting in association with a foreign power.

Officials said the two plots were separate, but the senior official briefed on the threat said British law enforcement is now trying to determine whether the same entity was directing both plots.  

The CIA and the U.S. National Intelligence Director’s office did not respond to requests for comment.

Some information about one of the two plots came to light early Sunday local time.

In the first announcement of arrests, Metropolitan Police said they took five men into custody, four of whom are of Iranian descent, in connection with what they called “an alleged terror plot in the U.K.”

The men range, who are 29 to 46, were arrested in various areas around the U.K. — including Swindon, London, Stockport, Rochdale and Manchester — under the Terrorism Act “on suspicion of preparation of a terrorist act,” police said. The age and the nationality of the fifth man is still being determined.

All remain in police custody. A motive was not immediately clear.

Police said a “fast moving” investigation into the first potential attack was underway. Counterterrorism police alleged the first group was targeting a specific site but declined to say where.

Details about the other purported attack plan have not been revealed.

Home Secretary Yvette Cooper called the two attacks “major operations” and said they reflect “some of the biggest counter-state threat and counterterrorism operations that we have seen in recent years,” according to video of the statement from Sky News. She also called the ongoing investigation “immensely important.”

Iranian nationals in the past have targeted U.K.-based Iranians. In one case, an independent television network named Iran International — which broadcasts in Farsi and had been critical of the Iranian government — moved from London to the United States after its journalists received state-backed threats from Iran, the BBC reported in 2023.

According to an ITV News investigation of that plot, the Islamic Revolutionary Guards Corps planned to kill two journalists at the network using a people smuggler, whom they paid $200,000 to carry out the attack. The plan was ultimately foiled when the smuggler became a “double agent” for an unnamed Western intelligence agency, according to the investigation.

In March 2024, another Iran International journalist was targeted and stabbed outside his London home, The Associated Press reported at the time. Two Romanian men were later charged in the attack.

The U.K. has responded to 20 Iran-backed plots since the start of 2022, which present “potentially lethal threats to British citizens and UK residents,” U.K. Minister of State Dan Jarvis said in an update last month, citing MI5 officials.

Jarvis said Iran is targeting dissidents, media organizations and journalists reporting on the violent oppression of the Iranian regime.

He added that Iran could also be planning attacks on Jewish or Israeli target, citing a “long-standing pattern of targeting Jewish and Israeli people internationally by the Iranian Intelligence Services.”

“It is clear that these plots are a conscious strategy of the Iranian regime to stifle criticism through intimidation and fear,” Jarvis said.