The U.S. State Department says Iran has continued “unabated” a brutal repression of its citizens, despite international condemnation and the country's increased isolation.

State Department spokesman Mark Toner made the comment Tuesday in a statement in which he welcomed a report from a U.N. special investigator.

Special rapporteur Ahmed Shaheed cited alleged human rights abuses, including prolonged detentions of political dissidents and unlawful executions, in an interim report that is being presented to the U.N. General Assembly this week.

The U.N. Human Rights Council voted in March to create the special investigator position for Iran, amid reports of the arrest and imprisonment of hundreds of political opposition leaders.

However, Tehran rejected the probe and has refused to allow Shaheed to enter the country.

The report and U.S. reaction to it have come at a time of heightened tensions between Washington and Tehran, following an alleged Iranian plot to kill the Saudi ambassador to the United States .

The U.S. Justice Department announced last week that it had broken up the suspected plot. However, Iranian President Mahmoud Ahmadinejad accused the U.S. of fabricating the incident in an attempt to cause a rift between his country and Saudi Arabia.