US President Joe Biden called to thank Qatar’s Emir Sheikh Tamim al-Thani for his help in releasing five Americans held in Iran, the two countries announced Tuesday.

The United States agreed in August to allow the release of $6 billion blocked in South Korea and five Iranian regime agents in US prisons to free five American Iranian dual nationals arrested and held in Iran.

Qatari Emir’s office highlighted the call by issuing a statement saying, "During the call, the strategic relations between the two countries and aspects of supporting and strengthening them in various fields were reviewed.”

The White House said the two leaders "discussed their commitment to deepen defense and security cooperation in the region."

Many US lawmakers and analysts criticized the White House for having agreed to pay the “largest ransom” in history and warned that such a large monetary reward for hostage taking will inevitably endanger more Americans around the world.

Qatar is considered a US ally in the region by hosting American military forces but is also one of the few friends Iran has among Arab countries. Last year, Biden designated Qatar as a major non-NATO ally of the United States, fulfilling an earlier promise that he had made to them.

The prisoner release deal, preceded by a US approval to free $2.7 billion of Iran’s money blocked in Iraq is seen as a step to reduce tension and facilitate talks over Iran’s nuclear program.

Qatar has recently held separate bilateral meetings with the United States and Iran that touched on Iran's nuclear program and US concerns about Iranian drone transfers to Russia, sources have told Reuters.