President Trump said Wednesday that Iran is planning a "sneak attack" on U.S. troops or "assets" in Iraq, warning the country will pay a "heavy price" if this happens.

The president made the abrupt announcement in a tweet Wednesday afternoon, coming amid lingering tensions between the two countries over past confrontations as well as the coronavirus pandemic.

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"Upon information and belief, Iran or its proxies are planning a sneak attack on U.S. troops and/or assets in Iraq. If this happens, Iran will pay a very heavy price, indeed!" Trump tweeted.

Trump’s tweet came soon after he attended an intelligence briefing at noon at the White House.

Sources told Fox News that the U.S. believes Iranian-backed proxies were planning the sneak attack, and that Trump's tweet was a warning to the Iranian leadership to tell their proxies to back down or face consequences

In late March, Secretary of State Mike Pompeo stated that Iran had refused American aid for addressing the coronavirus pandemic.

Pompeo also condemned Iranian leader Ayatollah Ali Khamenei for spreading conspiracy theories that the U.S. was responsible for the outbreak, and pointed out Iran's own misdeeds that exacerbated the spread of the virus.

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The latest tension comes several months after hostilities between the U.S. and Iran that included an attack at the U.S. Embassy compound in Iraq that U.S. officials blamed on Iran. In response, the U.S. carried out a strike that resulted in the death of Iranian Gen. Qassem Soleimani.

Prior to the embassy attack, U.S. airstrikes against an Iranian-backed Shiite militia in Iraq, which the U.S. military said was retaliation for the killing of an American contractor in a rocket attack on an Iraqi military base that it had blamed on the militia.

Fox News' John Roberts and The Associated Press contributed to this report.