The Trump administration has put a stop to U.S. purchases of nuclear materials from Iran, a policy that first began under the Obama administration in an attempt to ensure Iran remains in compliance with the landmark nuclear deal, according to U.S. officials who spoke to the Washington Free Beacon.

The Obama administration sparked controversy in Congress and the national security world when it announced in late 2016 that it would spend more than $8 million dollars to purchase Iranian heavy water, a nuclear byproduct, in a bid to keep the Islamic Republic in line with restrictions on these materials imposed under the nuclear agreement.

The Obama administration, in what lawmakers described as a "potentially illegal" taxpayer-funded transaction, paid at least $8.6 million to purchase 32 metric tons of heavy water from Iran. The nuclear byproduct can be used to produce weapons-grade plutonium, which is why restrictions were initially placed on Tehran's stockpile.

The transaction occurred via an offshore third-party, according to U.S. officials, who made clear at the time that it would engage in further purchases if they were needed to help keep Iran in compliance with the nuclear deal.

After leaving the door open to additional purchases, senior Trump administration officials confirmed to the Free Beacon on Wednesday that the U.S. government would no longer engage in these nuclear transactions with Iran, a major policy shift that sources say is part of an effort to crackdown on Iran's access to U.S. funds.

Lawmakers and other insiders had viewed the $8.6 million payment to Iran as a scheme to give Iran access to U.S. currency as part of an incentive package aimed at keeping it in compliance with the nuclear deal. The former administration stonewalled several attempts by lawmakers to discern the full details of the transaction.

Trump administration officials told the Free Beacon they have informed Iran that it is now solely responsible for maintaining compliance with the nuclear deal.

"No, the United States is not planning to purchase any Iranian heavy water," a White House National Security Council spokesperson told the Free Beacon. "We have made it clear to Iran that it is their responsibility to remain under their heavy water limit in the JCPOA," or Joint Comprehensive Plan of Action, the official title of the nuclear agreement.

A State Department official confirmed this shift in policy to the Free Beacon following a request for further information.

In May, House lawmakers approved a bill spearheaded by Rep. Ron DeSantis (R., Fla.), to outlaw all future purchases of Iranian heavy water by the United States. Democrats in the Senate opposed a similar measure due to concerns that it would conflict with U.S. efforts to preserve the nuclear agreement.

One source familiar with the administration's thinking on the policy shift told the Free Beacon it is part of a larger effort to take a tougher line towards Iranian efforts to gain further access to cash assets.

"This is another place where the Trump administration is saying ‘no' to Iranian extortion and blackmail," said the source, a veteran Middle East policy expert who routinely works with congressional offices on the Iran issue.

"Iran was deliberately overproducing heavy water and then telling the U.S. ‘buy it from us or it'll blow up the deal'," the source said. "The Obama administration paid, effectively rewarding Iran for violating the nuclear deal. The Trump administration refused to let the Iranians hold the deal hostage."

At the time the Obama administration was orchestrating the cash transaction, lawmakers were intentionally being kept in the dark, the Free Beacon first reported.

Current CIA Director Mike Pompeo, then a member of the House Intelligence Committee, told the Free Beacon at the time that the former administration was seeking to subsidize Tehran's nuclear program.

"The Obama administration's deal with the Mullahs in Tehran to purchase heavy water demonstrates a disturbing, potentially illegal, willingness of the administration to subsidize Iran's nuclear program," Pompeo told the Free Beacon. "This purchase allows the Iranians to offload previously unsellable product and it destigmatizes the act of doing business in Iran."

The purchase was "made without explanation as to how Iran will receive these funds or what steps the administration is taking to prevent what will almost certainly be U.S. taxpayer dollars from possibly being used to support terrorist activities, Syrian dictator Bashar al-Assad, or Iran's ballistic missile program," Pompeo said at the time.