TEHRAN, Iran (AP) — Iran’s foreign ministry said Monday it has sent the United States a list of names it is demanding in a proposed prisoner swap, opening a potential new channel with Washington amid recent growing tensions.

Iran did not detail the names it relayed, but Foreign Minister Mohammad Javad Zarif said he hoped to hear soon “good news” about the release of Iranian scientist Masoud Soleimani. U.S. federal authorities arrested Soleimani last year on charges that he had violated trade sanctions by trying to have biological material brought to Iran. Zarif said he raised the issue last month in his visit to New York to attend the U.N. General Assembly, according to the semi-official Fars news agency.

Ministry spokesman Abbas Mousavi said the Islamic Republic has relayed which Iranians should be included in the suggested swap with the United States and other Western nations. Iran holds several American nationals and did not detail whom it would consider freeing.

“We have handed over a list of names (to the United States) who must be freed,” Mousavi said, in a briefing with reporters. “We hope that these efforts, if paired with good will, would pay off soon and we would see freedom of Dr. Soleimani and other Iranians from the Americans’ captivity.”

Iran contends Soleimani and others were detained over what they called “baseless” accusations of bypassing unilateral American sanctions on Iran. It’s not clear how many other Iranians the U.S has detained, and there was no immediate American reaction.

Tensions between Iran and the United States have steadily escalated since President Donald Trump pulled the United States out of the 2015 nuclear deal last May and re-imposed sanctions on Iran. Prosecutors in Atlanta got an indictment the following month against Soleimani, who works in stem cell research, hematology and regenerative medicine. U.S. officials revoked his visa and arrested him in October when he landed in Chicago.

The U.S. blames Iran for a series of mysterious oil tanker attacks this year and alleges it carried out last month’s attack on the world’s largest oil processor in Saudi Arabia, which caused oil prices to spike by the biggest percentage since the 1991 Gulf War.

Iran denies the accusations and has warned any retaliatory attack targeting it will result in an “all-out war,” as it has begun enriching uranium beyond the terms of its 2015 nuclear deal. Iran also shot down a U.S. military surveillance drone and seized oil tankers.

A prisoner swap could offer a breakthrough following a pair of conciliatory moves.

A month ago, the U.S. deported Iranian Negar Ghodskani who was brought to the U.S. to face criminal conspiracy charges. She was sentenced to time served for conspiracy to illegally export restricted technology from the U.S. to Iran.

In June, Iran released Nizar Zakka, a U.S. permanent resident from Lebanon who advocated for internet freedom and has done work for the U.S. government. He was sentenced to 10 years on espionage-related charges and was freed after serving less than four years.

However, in May, Iran sentenced former U.S. Navy cook Michael R. White from Imperial Beach, California, to 10 years in prison in Iran, becoming the first American known to be imprisoned there since Trump took office.

Three other American citizens are known to be held in Iran, though Iran does not recognize their dual nationality

Iranian-American Siamak Namazi and his octogenarian father Baquer, a former representative for the U.N. children’s agency UNICEF who served as governor of Iran’s oil-rich Khuzestan province under the U.S.-backed shah, are both serving 10-year sentences on espionage charges.

Iranian-American art dealer Karan Vafadari and his Iranian wife, Afarin Neyssari, received 27-year and 16-year prison sentences, respectively.

Chinese-American graduate student Xiyue Wang was sentenced to 10 years in prison for allegedly “infiltrating” the country while doing doctoral research on Iran’s Qajar dynasty.

Iranian-American Robin Shahini was released on bail in 2017 after staging a hunger strike while serving an 18-year prison sentence for “collaboration with a hostile government.” Shahini has since returned to America and is now suing Iran in U.S. federal court.

Former FBI agent Robert Levinson, who vanished in Iran in 2007 while on an unauthorized CIA mission, remains missing. Iran says that Levinson is not in the country and that it has no further information about him, though his family holds Tehran responsible for his disappearance.

Others held with Western ties include Nazanin Zaghari-Ratcliffe, a British-Iranian woman who is serving a five-year prison sentence for allegedly planning the “soft toppling” of Iran’s government while traveling with her young daughter. Her daughter left Iran for Britain last week.