Five Americans imprisoned in Iran have been placed under house arrest in the first step of a planned prisoner exchange between Tehran and Washington that will include the release of roughly $6 billion in Iranian government assets blocked under U.S. sanctions, according to a lawyer for one of the prisoners.

If the proposed agreement goes through, Iran will be allowed to access the funds only to buy food, medicine or other humanitarian purposes, in accordance with existing U.S. sanctions against the country. Under the agreement, Qatar’s central bank will oversee the funds.

[This is not a prisoner swap. It’s a ransom payment. The US will transfer Iranian nationals in prison for the five Americans, but the big value for Iran is the access to the frozen funds, which came from the sale of oil under embargo rules. — Ed]