The deal would involve "significant" sanctions relief and the unfreezing of Iranian assets, in exchange for Iran agreeing to dismantle its nuclear program and hand over its nuclear material, the official said.

"I feel very good about the deal. I think the president has gotten to a very good spot," the senior official told reporters in a call, speaking on condition of anonymity.

"We're not quite at the finish line yet, but we are very close,"

A location and date for any deal signing had not yet been decided although Europe, which Trump had suggested, was a possibility, the US official said.

"We do expect us to be signing this agreement over the next few days. I can't give you an exact date," the official added.

"If I were to give you a confidence that we were going to be signing this agreement, I maybe would have said 75 percent this morning, it's probably more like 80-85 percent now, but it's not 100 percent."

The path to a deal began to clear as Iran agreed to "specificity" on how its enriched uranium would be disposed, the official said.

Washington also believed that Iranian control over the critical Strait of Hormuz had weakened, added the official.

Lebanon would also be included in the deal, a key issue that has threatened to unravel the process in the past as Israel continued to strike Iran's Hezbollah allies there.

"It includes Lebanon, it includes Iran, it includes the Gulf Coast countries, and includes Israel," the official said.