DUBAI, United Arab Emirates (AP) — Iran has put five Iranian-American prisoners to house arrest, a U.S.-based lawyer said Thursday, a move coming as Tehran for months has suggested a prisoner swap was possible between it and Washington. Iran did not immediately acknowledge the move.

The move comes amid months of heightened tensions between Iran and the U.S. A major American military buildup in the Persian Gulf is underway, with the possibility of armed U.S. troops boarding and guarding commercial ships traveling through the crucial Strait of Hormuz, through which 20% of all oil traded passes.

It remains unclear whether the Iranian-Americans’ transfers reflect significant progress in a possible prisoner swap between the two countries. Iran in past months has overstated progress in talks, likely conducted with mediation from Oman and Qatar, on a potential trade.

The U.S. in March called remarks by Iranian Foreign Minister Hossein Amirabdollahian that a deal for a swap was close a “cruel lie.”

U.S.-based lawyer Jared Genser acknowledged the move, identifying three of the prisoners as Siamak Namazi, Emad Shargi, and Morad Tahbaz. Genser did not identify the fourth and fifth prisoners.

The U.S. State Department declined to immediately comment.

Lee reported from Washington.