Federal prosecutors in the United States have charged three men they describe as Iranian-backed operatives over their alleged role in nearly 20 attacks and attempted attacks across the U.S. and Europe, including a plot targeting the British airbase RAF Fairford, which has housed American bombers.

The Department of Justice said on Tuesday that the three men acted in support of Iran's Islamic Revolutionary Guard Corps and Iraq's Kataib Hezbollah, both designated terrorist organizations by Washington. An eight-count superseding indictment unsealed in Manhattan named Mohammad Baqer Saad Dawood al-Saadi, Mohsen Mohajeri and Mohammad Ali al-Hassani, who face terrorism-related offenses.

Prosecutors say al-Hassani, a 35-year-old Iraqi national, directed others to drive to RAF Fairford in vans, some of which carried barrels of fuel. They say he had earlier paid the group to buy metal objects that could serve as shrapnel and to disguise the vans as fuel delivery vehicles. Police were called to the base in September after a local farmer reported seeing a group of men with several white vans engaged in suspicious activity.

Seven men were arrested in connection with the episode and all were released on bail. Two were subsequently re-arrested on suspicion of assisting Iran's intelligence service and charged under Britain's National Security Act. Days after the incident, the U.S. withdrew all of its B-1 bombers from Fairford.

Al-Saadi, 32, who holds Iranian and Iraqi citizenship, is accused of passing coded messages to al-Hassani and Mohajeri, a 48-year-old Iranian, to coordinate the plot, including in phone calls to his mother and sister in Iraq using coded language. Al-Saadi is already in jail in New York; prosecutors did not disclose the whereabouts of the other two men.

The alleged campaign included the nonfatal stabbing of two Jewish men in London in April and arson attacks on synagogues, Israeli businesses and Jewish schools elsewhere in Europe, as well as preparations for an attack on a Manhattan synagogue. U.S. authorities first detailed charges against al-Saadi in May, accusing him of directing others to attack U.S., Israeli and Jewish targets and to kill Americans in retaliation for the U.S.-Israel war on Iran. He pleaded not guilty in June and has been held without bail.

"These defendants helped orchestrate a campaign of terror on behalf of terrorist organizations affiliated with Iran that targeted Jewish communities in Europe and the United States, and the British military base, RAF Fairford, housing American service members," said Manhattan U.S. Attorney Jamie McDonald. Attorney General Todd Blanche said anyone who plans a terrorist plot on a military base housing American service members "will be prosecuted by the United States government." Iran has strongly denied any involvement in the Fairford incident. The charges are allegations, and the defendants are presumed innocent unless proven guilty in court.