New York, September 24 (RHC)-- At least a dozen Iranian students who were set to begin graduate programs in engineering and computer science say their visas were abruptly canceled and they were barred from their flights to the United States this month.

The sudden batch of visa cancellations, which came at a time of heightened tensions between the United States and Iran, set off a scramble by university officials, lawmakers, the students' union and Iranian-American advocates to figure out what had happened.

The State Department said that there had been no change in policy regarding student visas, and higher-education officials say that visa problems arise every fall for some of the hundreds of thousands of international students who travel to attend U.S. colleges and universities.

But the students, most of whom were headed to schools in the University of California system, say their visas were revoked at the last minute, without any warning or explanation.  Most were prevented from boarding flights in Iran, and others from boarding connecting flights in the Persian Gulf.  One was detained at Boston Logan International Airport and then turned back on the next flight out.

Many of the students said that a State Department webpage showed their visa cases had been updated around August 30th, and they were prevented from boarding in early September.  All of that occurred before a September 14 attack on two key Saudi oil installations, which has escalated a standoff between the United States and its ally Saudi Arabia against Iran.

A law enacted in 2012 under President Barack Obama requires the U.S. government to deny visas to Iranian students whose course work would prepare them to work in the energy or nuclear sectors in their home country.  Consular officials have wide discretion on how to interpret the statute and put it in place, said Jamal Abdi, the president of the National Iranian American Council, a Washington group.

Most Iranians cannot obtain visas to travel to the United States because of the travel ban on visitors from their country.  But there are narrow exemptions, including for students.  Most of the students who were barred had been given single-entry visas, and were prepared to go years without seeing family members who would not have been able to visit them.

In phone interviews and e-mails, the students said they were extremely dissapointed.  Some had left high-level jobs or sold their homes, or had turned down opportunities in Europe or Canada. Most said their studies had been fully funded, and many had been set to begin teaching or research positions in addition to their studies.

"I feel I'm damaged emotionally, financially, academically," said Peyman, 23, who was supposed to begin a degree in electrical engineering at the University of California at San Diego.  He asked to be identified only by his first name because he did not want to jeopardize his chances of getting another visa.

Peyman said that he had been barred from a connecting flight in Qatar this month and that an airline employee had scrawled "CANCELED" across his visa in pen, saying the instructions to do so had come from the Department of Homeland Security.

The State Department does not release data on visa revocations, and the department said that it could not release information about individual cases.