WASHINGTON -- The Obama administration is increasingly questioning the long-term stability of Tehran's government and moving to find ways to support Iran's opposition "Green Movement," said senior U.S. officials.

The White House is crafting new financial sanctions specifically designed to punish the Iranian entities and individuals most directly involved in the crackdown on Iran's dissident forces, said the U.S. officials, rather than just those involved in Iran's nuclear program.

U.S....