Leading U.S. officials are expressing concern about newly disclosed efforts by the Obama administration to play down the terrorism threat posed by Iran in an official report issued this year.

Director of National Intelligence James Clapper admitted in a recent letter to top senators that the administration wrongly excluded references to the global terrorism threat posed by Iran and its terror affiliate Hezbollah in the 2015 World Threat Assessment of the U.S. Intelligence Community.

"A specific reference to the terrorist threat from Iran and Hizballah—which was not included in any of the drafts of the testimony [offered before lawmakers]—would have been appropriate for the 2015 Assessment, but the lack of its inclusion is in no way a change in the [intelligence community’s] assessment," Clapper wrote in a June 3 letter to top senators.

Clapper’s letter came in response to an earlier letter from a delegation of senators who were seeking to discover why the Obama administration excluded references to Iran’s global terrorist operations.

"Despite ongoing nuclear negotiations and the administration’s evolving policy towards the Iranian regime, we are perplexed that your annual assessment contains no meaningful reference to the chaos that Iran manufactures through its support for terrorist groups and proxy organizations, which raises serious questions about the credibility of this annual exercise," Sens. Dan Coats (Ind.), Tom Cotton (Ark.), Susan Collins (Maine), James Risch (Idaho), and James Lankford (Okla.) wrote in an April 28 letter to Clapper.

Some critics accuse the Obama administration of downplaying the terrorist threat posed by Iran and its proxies in order to appease the Islamic Republic and preserve the ongoing talks aimed at inking a wide-ranging nuclear deal.

Coats said that the Obama administration cannot overlook Iran’s longstanding financial support for terrorist groups across the region.

"Any objective reading of Director Clapper’s annual threat assessment leaves the impression that terrorist violence is limited to Sunni extremists, raising serious doubts about the credibility of the analysis," Coats said. "I welcome Director Clapper’s recognition of that error, but I remain concerned about the administration’s priorities."

"Al Qaeda, ISIS, and their respective affiliates represent significant threats to our nation, but this administration cannot overlook Iran’s support for terrorism, especially as it concludes an unwise nuclear deal with a regime that undermines American interests at every opportunity," Coats added. "If Director Clapper expects us to take future assessments seriously, he must strive to fairly inform policymakers and educate the American people about the threats we face, without editorializing."

Sen. Mark Kirk (R., Ill.), one of the leading critics of the administration’s diplomacy with Iran, said that U.S. concessions to Iran at the negotiating table would only embolden its rogue behavior.

"As the Obama administration further concedes to Iranian demands for a nuclear deal with weak terms, Director of National Intelligence Clapper’s letter soberly reminds Congress that Iran remains a grave and gathering threat," Kirk said.

"No American lawmaker will be able to claim ignorance when a final deal’s sanctions relief allows Iran to funnel billions to Hezbollah, Syria’s Assad regime, Shia militias in Iraq, Houthi militants, and other destabilizing actors in the region," he said.

One senior congressional staffer who has long worked on the issue said that under the Obama administration, official assessments have repeatedly sought to downplay the Iranian threat.

"Whether you’re talking about the U.S. Intelligence Community’s annual Worldwide Threats assessment, the Pentagon’s ever-shrinking annual report on Iran’s military power, or official hints that the pro-terror Iranian regime could somehow be an ally against terrorism in the Middle East, the Obama Administration seems eager to downplay the dangers posed by Iran as negotiators close in on a comprehensive nuclear agreement," said the source, who was not authorized to speak on the record.

While Clapper admitted that a full assessment of Iran’s terror activities was wrongly missing from the 2015 report, he reminded senators in his letter that the intelligence community is aware of Iranian action against the United States.

"The United States Intelligence Community continues to assess that Iran and Hizballah directly threaten the interests of the United States and our allies and that Hizballah remains a global terrorist threat," Clapper wrote to senators.

However, senators are still seeking to obtain both classified and unclassified reports on "Iran’s support for terrorism and the threat posed by Shia militants."

They also requested that Clapper "inform us whether previous drafts of the unclassified assessment contained information regarding Iran’s support for terrorism; the justification for removing those references; and who made the decision to remove them," according to the original letter to the DNI.

Meanwhile, as negotiations with Iran reach a self-imposed June 30 deadline, Iranian officials are lashing out at members of Congress for trying to obstruct a deal.

The comments come on the heels of reports that the Obama administration has conceded significant ground to Iran, potentially enabling Tehran to gain economic sanctions relief without disclosing its past military nuclear work.

"There are streams within the U.S. which don’t want the negotiations to produce results and all their efforts are aimed at stopping the negotiations," Morteza Sarmadi, Iran’s vice minister of foreign affairs, was quoted as saying on Tuesday.