The United States has blamed Iran for an upswing in attacks against U.S. forces in Iraq over the summer that made June the deadliest month for U.S. personnel there since 2008. The United States also accuses Tehran of supplying weapons to Afghan militants, although on a far smaller scale than in Iraq.
In recent years, Suleimani's Quds Force has been "meddling in more places," the first senior U.S. official said.
"There are opportunities they think they can exploit in various places in the Middle East, that either they've got some foothold, and we're on one side, and they're on the other," the official said.
Vali Nasr, a professor of international politics at Tufts University, said the alleged plot cited by U.S. officials tracked with what appeared to be "far more aggressive Iranian behavior everywhere else."
He also cited Syria, Iraq, Lebanon, and Afghanistan.
"For some, it might be this news came in the context of a trendline that they were seeing with Iran," Nasr said.
U.S. officials have told Reuters they believe Suleimani is connected to the latest U.S. plot.
"Whether he is doing this like other things on his own or whether this is the direction of Khamenei, we can't say right now," the first U.S. official said. "It's a problem no matter what."
Nasr said he doubted the Quds Force would be doing something as risky as a plot on U.S. soil without political clearance from above.
Some Iran watchers were stunned that Tehran would choose to carry out an attack on U.S. soil, a potentially dangerous departure from past protocol. But U.S. officials following Iran told Reuters the behavior was consistent with the activities by the Quds Force and Suleimani.
"It makes a huge difference to us that it's on U.S. soil. But Iran has been, with only the thinnest of veils, seeking to kill U.S. troops and U.S. government individuals for years," the military official said.