The White House secretly reached out to Iran to establish a direct channel to discuss swapping prisoners, a diplomatic gambit signaling a change in the Trump administration’s hardline stand on the Islamic Republic, according to a report Thursday.

But Iran did not respond to the overture despite at least three other attempts and has refused to communicate with US officials, leaving the fate of several Americans held in the country uncertain, the Wall Street Journal reported.

The approach marked the first time since President Trump entered the White House that his administration has attempted to pull off a prisoner exchange, the report said.

Instead, it has been hardening its approach to the country by criticizing a 2015 nuclear pact between Iran and the United States and other world powers as the “worst deal ever” and by accusing the regime of creating chaos in the Middle East by meddling in other nations’ affairs.

Trump was also critical of the last prisoner exchange between the US and Iran when the Obama administration in January 2016 released seven Iranians in a swap for four dual-citizenship Americans being held in Iran.

The same day, the US sent a $400 million cash payment to Tehran that was part of funds frozen by Washington since the 1970s, a delivery Trump called a “ransom” payment.

“Despite the Trump administration’s outward bluster toward Tehran, they’ve shown a surprising willingness to try to engage the Iranians behind the scenes,” Karim Sadjadpour, an Iran expert with the Carnegie Endowment for International Peace, told the newspaper.

The State Department said “that they had opened the door and reached out to Iran several times but there is no response,” according to Hua Qu, wife of Xiyue Wang, a Princeton University graduate student who was arrested in 2016 and sentenced to 10 years for spying.

Wang, an American citizen of Chinese descent, is being held along with three dual American-Iranian citizens: Baquer and Siamak Namazi, a father and son detained on charges of “collusion with an enemy state,” and Karan Vafadar and his wife, Afarin Nayssari, who is a permanent resident of the United States.

The State Department didn’t comment directly about the outreach.

“We look for every opportunity we can to bring attention to the fact that we would like to see American prisoners held unjustly in Iran released and that is done through a variety of mechanisms,” Steve Goldstein, undersecretary of state for public diplomacy and public affairs, told the Wall Street Journal.

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Iran’s United Nations mission didn’t respond to questions about how many Iranians are being held in the US. But activist groups said a dozen Iranians are imprisoned on charges related to evading US sanctions.