The Democratic members of the Gang of 8, a group of congressional leaders who receive high-level briefings on intelligence matters, urged President Trump in a March 27 letter to consult Congress before ordering strikes on Iran or taking other actions that could lead to war. The lawmakers cited recent media reports that suggested the administration was preparing for military action.

The president tweeted on Wednesday that the U.S. had received intelligence regarding an Iranian-backed "sneak attack" on U.S. forces in Iraq, and warned Tehran of likely retaliation.

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

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Iranian foreign minister Javad Zarif later responded to the president's warning, writing in his own tweet, "Don't be mislead [sic] by usual warmongers…Iran starts no wars, but teaches lessons to those who do."

It was among the most charged rhetorical exchanges since the January 3 U.S. strike on Iranian general Qassim Soleimani, who was killed alongside nine others soon after arriving at Baghdad International Airport.

Iran's subsequent retaliatory strike on January 8 injured more than 100 U.S. soldiers, most of whom suffered from traumatic brain injuries. While the U.S. did not respond militarily, it has maintained and in recent weeks heightened its campaign of maximum pressure on Tehran, ordering new sanctions even as Iran's economy has been crippled by a massive domestic outbreak of COVID-19. To date, Tehran's health ministry has reported more than 47,000 cases and over 3,000 deaths, although public health officials believe the toll may be much higher.

The Democratic lawmakers' letter, which was obtained by CBS News, warned that the administration had legal obligations to keep congressional leadership informed of potential military escalation.

"While there are well-understood and narrow self-defense exceptions, the Constitution and U.S. law require you to consult with Congress before engaging in military action or actions likely to lead to war," they wrote. The letter was signed by House Speaker Nancy Pelosi, Senate Minority leader Chuck Schumer, House Intelligence Committee chairman Adam Schiff and Senate Intelligence Committee Vice Chairman Mark Warner.

The lawmakers also said the administration had "largely failed" to date to fulfill those legal obligations, citing the January strike on Soleimani. Trump administration officials said the strike was carried out to forestall an "imminent" attack on U.S. interests in the region, though that justification received bipartisan criticism from lawmakers who said subsequent briefs on the intelligence underlying the attack were unsatisfying. The Gang of 8 Democrats said at the time that they were not briefed in advance of the strike, though some Republican allies of the president, including South Carolina Republican Lindsey Graham, were.

Asked at an afternoon Coronavirus Task Force briefing about the potential attack from Iran, Mr. Trump said the Iraqi government had been kept informed of the plot and that the U.S. administration had "very good information" about it. He also said his administration's tough policies could force Iran to the negotiating table.

"It was led by Iran – not necessarily Iran, but by groups supported by Iran. But that, to me, is Iran," Mr. Trump said of the alleged attack. "And we're just saying, 'Don't do it. Don't do it.' It would be a very bad thing for them if they did it."

Secretary of Defense Mark Esper, who was also present at Wednesday's briefing, said Iran had refused U.S. offers of aid and assistance during the COVID-19 outbreak even as it continued to engage in malign activities in the region. "We empathize for the Iranian people," Esper said, "[T]hey clearly have been hit hard."

"The important thing is that the Iranian government should focus on them and stop this malign behavior that they've been conducting now for over 40 years," he said.

"I happen to think they want to make a deal," Mr. Trump added. "I think they're dying to make a deal."