The top Republican on the House Armed Services Committee says he is "convinced" there is cause for concern around Iran's activists following a pair of briefings on the Gulf nation.

“I am convinced that the information and warnings that we have collected are of greater concern than the normal Iranian harassment activity that we’ve seen in the Persian Gulf and the surrounding area,” Rep. Mac Thornberry William (Mac) McClellan ThornberryTrump payroll-tax deferral for federal workers sparks backlash Overnight Defense: Woodward book causes new firestorm | Book says Trump lashed out at generals, told Woodward about secret weapons system | US withdrawing thousands of troops from Iraq Top Armed Services Republican 'dismayed' at Trump comments on military leaders MORE (R-Texas) told reporters Thursday.

“I don’t think it’s business as usual. It is cause for greater concern. ... and a great part of that concern relates to Americans being targeted.”

Several prominent senators on Thursday called for more information from the Trump administration after it pulled nonemergency U.S. personnel from Iraq as part of escalating tensions with Tehran.

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Sens. Lindsey Graham Lindsey Olin GrahamSenate GOP aims to confirm Trump court pick by Oct. 29: report The Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting Senate GOP sees early Supreme Court vote as political booster shot MORE (R-S.C.) and Patrick Leahy Patrick Joseph LeahyDemocrats shoot down talk of expanding Supreme Court Battle over timing complicates Democratic shutdown strategy Hillicon Valley: Russia 'amplifying' concerns around mail-in voting to undermine election | Facebook and Twitter take steps to limit Trump remarks on voting | Facebook to block political ads ahead of election MORE (D-Vt.) – the chairman and ranking member, respectively, of the Senate Appropriations Subcommittee on State and Foreign Operations – requested in a letter to Secretary of State Mike Pompeo Michael (Mike) Richard PompeoTreasury sanctions individuals, groups tied to Russian malign influence activities Navalny released from hospital after suspected poisoning Overnight Defense: Pentagon redirects pandemic funding to defense contractors | US planning for full Afghanistan withdrawal by May | Anti-Trump GOP group puts ads in military papers MORE that he brief senators on the decision, saying they had "great concern" about the move.

Lawmakers are specifically asking for the administration to explain the intelligence it received about Iran that warranted the quick deployment of a bomber task force and carrier strike group to the region earlier this month. Bolton said at the time that the move was in response to “a number of troubling and escalatory indications and warnings” from Iran.

The Graham and Leahy letter also comes as Senate Minority Leader Charles Schumer Chuck SchumerCruz blocks amended resolution honoring Ginsburg over language about her dying wish Senate Democrats introduce legislation to probe politicization of pandemic response Schumer interrupted during live briefing by heckler: 'Stop lying to the people' MORE (D-N.Y.) on Thursday called for acting Defense Secretary Patrick Shanahan Patrick Michael ShanahanHouse Armed Services chairman expresses confidence in Esper amid aircraft carrier coronavirus crisis Boeing pleads for bailout under weight of coronavirus, 737 fallout Esper's chief of staff to depart at end of January MORE and Chairman of the Joint Chiefs Gen. Joseph Dunford to testify publicly before the Senate Armed Services Committee about intelligence concerning Iran.

“At this moment, the only thing that is abundantly clear about the administration's Iran policy is its lack of clarity and the lack of consultation with Congress and with the American people,” Schumer said.

Top congressional leaders later in the day received such a classified briefing but would not say whether they were satisfied with the information or whether alleged threats from Iran are credible.

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But Thornberry said the briefings he attended – one by U.S. Central Command officials and the other from Joint Chiefs of Staff officials, meetings open to all members of the committee – have left him confident the administration is making the right moves.

“There had to be a strong signal sent to Iran that we would defend ourselves if we are attacked,” he said. “I hope everybody can rally around that. Showing that we are willing to stand up and defend Americans was an important thing to do.”

He added that the number of planes and ships that the U.S. sends to the region is a decision “best left to the military. But the hope for me and pretty much everyone is that Iran decides it’s not worth attacking us ... and that can be a deterrent.”

Asked whether he was concerned that recent comments by President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE and national security adviser John Bolton John BoltonMaximum pressure is keeping US troops in Iraq and Syria Woodward book trails Bolton, Mary Trump in first-week sales Ex-NSC official alleges 'unprecedented' intervention by White House aides in Bolton book review MORE may escalate tensions with Iran unnecessarily, Thornberry said his sense is that “Iran is not hanging on every word that’s tweeted or said by Bolton or anybody else.”

“What they do watch is what we do. So I do think showing that we are willing to stand up and defend Americans was an important thing to do and hopefully deter any sort of attacks from happening.”

He added: “If we’re attacked, I expect our military forces will be in a position to respond. I hope that’s not what happens. ... It shouldn’t happen. I hope that the tensions start to diminish.”