The United States blacklisted an affluent Iranian business executive and what it described as his multibillion-dollar money-laundering network on Thursday, accusing them of selling oil for Iran in violation of the Western economic sanctions imposed over Iran’s disputed nuclear program.

The Treasury Department, which administers the government’s Iran sanctions, said the executive, Babak Morteza Zanjani, had conspired with the First Islamic Investment Bank of Malaysia and an international network of front companies stretching halfway around the world “for moving billions of dollars on behalf of the Iranian regime.”

The announcement, coming just a few days after diplomatic talks with Iran over the nuclear issue adjourned with no sign of progress, was the second high-profile Treasury action against those accused of violating the Iranian sanctions in less than a month.

On March 14, the Treasury blacklisted a Greek shipping tycoon, Dimitris Cambis, over what it called his scheme to acquire a fleet of oil tankers on Iran’s behalf and disguise their ownership to ship Iranian oil.