President Donald Trump’s “playing with fire” reaction Monday to news Iran had breached its limits on enriched uranium prompted Iran’s foreign minister to hit back by asking “seriously?” in a one-word Twitter response.

Mohammad Javad Zarif his response to a White House statement late on Monday when the U.S. government claimed: “There is little doubt that even before the deal’s existence, Iran was violating its terms.”

And Donald Trump, at a White House event, accused Iran of “playing with fire” after stockpiling more enriched uranium than is allowed under a 2015 international agreement.

He said: “They know what they’re doing. They know what they’re playing with, and I think they’re playing with fire. So, no message to Iran whatsoever.”

The White House, while saying it would continue its maximum pressure campaign until Iran’s leaders change course, did not explain how Iran could have been breaking the terms of an agreement before it was created.

Iran announced on Monday it had amassed more low-enriched uranium than permitted under its 2015 nuclear deal with world powers.

The Joint Comprehensive Plan of Action (JCPOA), more commonly known as the Iran nuclear deal, was reached between Iran and the United States, the UK, Russia, France, China, Germany and the EU in July 2015 – and the U.S. then agreed to lift nuclear-related sanctions on Iran.