Iran has issued a travel warning to its citizens against visiting arch-foe the United States, an official said, after the death of an Iranian national reportedly following a grilling by U.S. customs officials, AFP reported.

“Iranian citizens are advised to avoid non-essential travels to the US and, in case of visit, to exercise maximum caution,” foreign ministry spokesman Ramin Mehmanparast said in remarks reported by the ISNA news agency.

The US is a “high risk” destination for Iranian travelers, he said citing a “targeted Iranophobia trend in the US and repeated incidents in which Iranian citizens are threatened and arrested there.”

His comments came after US media reported that an Iranian citizen, Daryoush Sarreshteh, 73, died two days after being subjected to “intense questioning” by US customs officials on arrival November 6 at Dulles International Airport.

Mehmanparast said the interrogation was “inhumane” and demanded a “precise investigation” by American authorities into the incident.

“A five-hour unusual and inhumane interrogation of an elderly man cannot be acceptable,” he said, adding that this ministry would follow up the case.

Iran and the United States have had no diplomatic relations for more than three decades, as the two continue the intense years-long dispute over Tehran’s controversial nuclear program.

On December 7, the U.S. State Department renewed its travel warning for Iran saying that American citizens “may be subject to harassment or arrest while traveling or residing in Iran.”

“Since 2009, Iranian authorities have prevented the departure, in some cases for several months, of a number of Iranian-American citizens, including journalists and academics, who traveled to Iran for personal or professional reasons. Iranian authorities also have unjustly detained or imprisoned US citizens on various charges, including espionage and posing a threat to national security. US citizens of Iranian origin should consider the risk of being targeted by authorities before planning travel to Iran. Iranian authorities deny the US Interests Section in Tehran access to imprisoned dual national Iranian-American citizens because Iranian authorities consider them to be solely Iranian citizens; access to US citizens is often denied as well,” the Department wrote in a posting on its website.

On November 4, 1979, an angry Islamic mob overran the US Embassy in Tehran, taking 52 Americans hostage.

The hostages were released on January 21, 1981, 444 days after the crisis began and just hours after President Ronald Reagan delivered his inaugural address. Many historians believe that hostage crisis cost Jimmy Carter a second term as president.