Neither action will change Americans' behavior much. Americans have been banned from doing business with Hezbollah since the U.S. declared it a foreign terrorist organization in the 1990s. Decades of U.S. sanctions against Syria have hampered energy trade between the two countries, and President Barack Obama blacklisted any new imports a year ago.
Sytrol had mostly exported to the European Union, but the bloc also declared an embargo against Syrian oil last year.
"Hezbollah's extensive support to the Syrian government's violent suppression of the Syrian people exposes the true nature of this terrorist organization and its destabilizing presence in the region," the Treasury Department's sanctions chief, David S. Cohen, said.
Asked what the latest U.S. action against Hezbollah might accomplish, the State Department's counterterrorism coordinator, Daniel Benjamin, said he hoped it would lead other countries to follow suit. "That would limit the amount of space for Hezbollah to operate in," he told reporters in a telephone briefing.
Ventrell said Iran's support for the Assad regime, including equipment to monitor opposition activity on the Internet, was "completely unjustifiable." He said that Iran fears losing its only remaining ally in the Middle East, Syria.
"Today's sanctions action sends a stark message: The United States stands resolutely against sales of refined petroleum product to Iran and will employ all available measures to bring it to a halt," he added. "Any business that continues to irresponsibly support Iran's energy sector or helps facilitate either nation's efforts to evade U.S. sanctions will face serious consequences."
The announcements came as Secretary of State Hillary Rodham Clinton was traveling to Turkey for weekend talks with top Turkish officials and Syrian opposition activists. The discussions will focus on forming a "common operational picture" to guide a democratic transition after President Bashar Assad leaves power, U.S. officials said.
Clinton will also boost humanitarian relief to tens of thousands of Syrians fleeing the country, said the officials, who spoke on condition of anonymity because they weren't authorized to speak publicly. They said the additional aid is expected to be worth $5.5 million. That brings total U.S. humanitarian relief to $82 million since the crisis began in March 2011.
Coordinating support for the Syrian opposition remains a challenge. The officials said Clinton was keen to understand Turkey's position as conditions inside Syria deteriorate and with rebel forces gaining strength and effectiveness.
The United States and its Western allies are stopping short of providing lethal assistance to the opposition, but it has become an open secret that several Arab countries are supplying weapons and ammunition.
The officials said Clinton would take what she learns in Istanbul from the Turks and the Syrian activists she meets and begin to discuss points of agreement with European foreign ministers in the coming days. A new "Friends of Syria" meeting will be held in late August or early September.