Three men, including one already jailed in the U.S., were accused by U.S. authorities Tuesday of being Iran-supported operatives who plotted nearly 20 attacks on Jewish communities in Europe and the U.S., as well as a planned assault on a British air base used by the U.S. Air Force.

Charges against Mohammad Al-Saadi, a dual Iranian-Iraqi national; Mohsen Mohajeri, an Iranian national; and Mohammad Ali Al-Hassani, an Iraqi national, were outlined in a superseding indictment unsealed in federal court in New York City.

Only Al-Saadi — an alleged pro-Iranian terrorist who is believed to have plotted attacks across Europe, Canada and the U.S., as first reported by NBC News — is in custody.

U.S. Attorney Jamie McDonald in New York said in a news release that Al-Saadi, who was arrested in the spring, continued to coordinate with his co-defendants in the days leading up to the attempted September terrorist plot at a British Royal Air Force Base in Fairford, where U.S. bombers and troops had been stationed.

“As alleged, 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 McDonald, whose office is handling the case.

“The threat presented by Iran and Iran-backed terrorist groups to America and our allies is not hypothetical — it is very real,” he added in the statement.

The new indictment offers fresh insight into an episode that has been shrouded in mystery for more than a month after five men were detained after midnight Sept. 27 on suspicion of explosives and terrorism offenses after three suspicious vans were spotted traveling toward the base in western England.

The Justice Department indictment alleges that Al-Hassani paid associates to carry out surveillance of RAF Fairford in August and paid several people to move forward with the plot in September “by procuring vans and barrels of fuel, researching the purchase of chemical accelerants, including large quantities of potassium chloride, and purchasing metallic objects that could be used as explosive shrapnel.”

The group even made custom decals to give the vans the appearance that they were used by a fuel company and a swimming pool supply business, authorities say.

Al-Hassani is alleged to have then tasked the people to go to the base with the fuel when U.K. law enforcement took the men into custody.

Al-Saadi was helping direct the RAF Fairford plot while he was in a U.S. prison, according to the indictment. He made video and phone calls to his family members in Iraq, who are alleged to have passed coded messages to Al-Hassani and Mohajeri.

In a July call with his sister, Al-Saadi asked, “What are we doing about all our old work?” — a reference to terrorist activity — according to investigators.

His sister replied, “It isn’t cancelled,” investigators said.

The indictment alleges that the three men conspired to use a network of contacts in the United Kingdom to commit terrorist attacks on behalf of an Iran-aligned terrorist network, which included Iran’s Islamic Revolutionary Guard Corps and Kata’ib Hizballah.

In June, Al-Saadi pleaded not guilty to charges that he plotted at least 18 attacks in Europe in retaliation for the U.S. and Israel’s war with Iran.

The U.S. government has designated Kata’ib Hizballah and the Revolutionary Guards as foreign terrorist organizations.