Trump made the remarks at a joint press conference with Italian Prime Minister Paolo Gentiloni Thursday after he was asked if he had "reason to suspect that [Iran is] cheating" on the deal. On Tuesday the administration notified Congress that Iran was continuing to comply with the terms of the deal, a notice that must be given every 90 days.
"I think they are doing a tremendous disservice to an agreement that was signed," said Trump, adding "we're analyzing it very, very carefully and we'll have something to say about it in the not-too-distant future."
Trump did not give any additional details about Iran's adherence to the pact.
The agreement puts limits on Iran's nuclear activities in exchange for the lifting of economic sanctions that for years crippled Iran's economy.
"An unchecked Iran has the potential to travel the same path as North Korea and take the world along with it," said Tillerson Wednesday.
Trump said on Thursday that the deal "shouldn't have been signed," and added that "I'm all for agreements, but that was a bad one -- as bad as I've seen negotiated."