President Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE on Wednesday warned that his administration would soon "substantially" increase sanctions on Iran after the country exceeded the uranium enrichment level limits laid out in the Obama-era nuclear deal.

"Remember, that deal was to expire in a short number of years. Sanctions will soon be increased, substantially!" Trump tweeted.

Trump claimed that Iran had "long been secretly" enriching uranium in violation of the 2015 nuclear agreement, formally known as the Joint Comprehensive Plan of Action. But the U.S. and international monitoring agencies had previously found Iran was abiding by the terms of the deal.

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Trump withdrew the United States from the nuclear agreement in 2018 and reimposed harsh sanctions on Iran. The accord was co-signed by France, Germany, England, Russia and China, and provided Tehran sanctions relief in exchange for limits on its nuclear program.

International inspectors and the deal’s signatories, including senior U.S. officials, had said prior to Trump's withdrawal that Iran was in compliance with the terms of the agreement. The United Nations's atomic watchdog filed a report in May that found Tehran was staying within the main restrictions of the deal.

But the Trump administration has ratcheted up sanctions on Iran over the course of the past year, hitting Iran's oil industry, its metals sector, its Revolutionary Guard and the supreme leader in an effort to isolate the country and cripple its economy.

In recent months, Tehran has made clear its intent to exceed the limits of the deal.

The international agency that monitors Iran’s compliance with the agreement confirmed Monday that Tehran has exceeded the agreement’s uranium enrichment level. It marked Tehran’s second major breach in as many weeks of the 2015 agreement.

Trump has been vague about his response to Iranian behavior. In recent months he has threatened the country with fiery rhetoric and has deployed additional troops to the region.

After Iran shot down a U.S. drone last month, the president initiated and then called off a retaliatory strike after he said he learned of the expected casualties.

Asked Wednesday how long he planned to wait before taking action against Iran, Trump was noncommittal.

"We’re going to see what happens with Iran," he told reporters in the Oval Office. "Iran is doing a lot of bad things right now and they better be very careful."