Washington (CNN) -- Venezuela's ambassador to the United States is defending his country's controversial airline service to the capitals of Syria and Iran -- both countries that are designated by the U.S. as state sponsors of terrorism.
The scheduled flights to Damascus and Tehran were cited by the U.S. State Department this month as a cause for concern, and U.S. Rep. Eliot Engel, D-New York, raised questions about the flights in an interview last week with Voice of America.
According to the State Department's latest country report on terrorism, which covers 2009, "President [Hugo] Chavez continued to strengthen Venezuela's relationship with state sponsor of terrorism Iran. Iran and Venezuela continued weekly Iran Airlines flights connecting Tehran and Damascus with Caracas."
A 2007 report went further, raising concerns about the travelers from Syria and Iran who might be onboard. It said in part, "Passengers on these flights were not subject to immigration and customs controls at Simon Bolivar International Airport" in Caracas.
It also noted that one passenger who bought a ticket on the route that year was Abdul Kadir, who was convicted this month of plotting a 2007 attack on fuel pipelines for New York's John F. Kennedy International Airport. He was arrested on a plane bound for Caracas and never made his connection for the flight to Iran.
Engel, the chairman of the Western Hemisphere subcommittee, told Voice of America last week, "I am very troubled about the flights into Damascus and Caracas. I believe that Iran is the largest supporter of terrorism of any country on the face of the earth."
In a written response to the concerns raised by Engel, Venezuelan Ambassador Bernardo Alvarez Herrera defended the state-owned airline, Conviasa.
"There is absolutely nothing untoward about these flights -- which take place between two countries that have shared diplomatic relations for over 50 years," Herrera wrote in the letter dated August 13. "One can also fly to Tehran from Frankfurt, Germany, amongst other cities, so I still remain confused as to why this should be of any concern. Should you or your staff want to see for yourself, I greatly encourage you to take one of the flights."
Contacted by CNN about the flight and its passengers, former CIA director Michael Hayden said, "The concerns are not just in the abstract. We saw people traveling who made us wonder."
Peter Brookes, a former deputy assistant defense secretary now with conservative think tank the Heritage Foundation, said passengers on the flight from Iran and Syria could include "people who probably ... are intelligence agents, probably Islamic Revolutionary Guards forces, Quds force, even Hezbollah terrorists."
Brookes pointed to Venezuela's proximity to U.S. interests in the Western Hemisphere and said, "I think the greatest concern is, there might be individuals -- terrorists, operatives, soldiers -- who might attack American interests, if the Iranian nuclear drive comes to a head."
An Iranian official did not reply to phone or e-mail messages requesting comment.
A Venezuelan official said passengers arriving from Iran and Syria go through normal customs and immigration checks, and there has never been any evidence that flights have carried suspected militants. He described it is a legitimate commercial route, whose passengers include businessmen and other civilian passengers.
When CNN tried to book a trip on the flight, it was unclear whether seats were available to the general public -- or whether the flight, which began in 2007, was even running at all.
An agent at Conviasa said a round-trip would cost $1,450, and the flights depart from Tehran on Thursdays and depart from Caracas on Tuesdays. But he then said, his computer showed no seats available for the next four Thursdays -- and after that, the flight was not offered.
Another Conviasa representative, reached the next day, said that while the flight from Caracas to Syria was still running, the continuing leg from Syria to Iran has not been operating for some time.
CNN's Pam Benson and Joann Sierra contributed to this report.