A former head of the North Atlantic Treaty Alliance (NATO) was denied electronic authorisation to enter the United States after his online application was rejected due to what he said was a trip to Iran.

Javier Solana, who headed the military alliance from 1995 to 1999 and served as the EU’s foreign policy chief until 2009, saw his renewal application on the Electronic System for Travel Authorisation (ESTA) denied for the first time.

The 75-year-old Spaniard believes this was due to a trip to Iran where he partook in negotiations for the now defunct 2015 nuclear deal.

A former foreign minister for Spain, Solana was scheduled to speak at an event in Washington hosted by the Brookings Institution, where he is also a fellow.

“I went as a representative for all those who negotiated,” Solana said, adding that “people must go to the most complicated countries to keep going with negotiations.”

“What seems most shocking to me is that these people be treated the same way as others [in terms of being allowed or denied entry].”

European nationals are expected to fill out an online application for entry to the US in trips that are three months long in duration or under.

In 2016, the fast-track authorisation was revisited by the Obama administration in response to restrictions decided by Congress.

Citizens from 38 countries who had visited Iran, Iraq, Syria, Libya, Somalia and Yemen would be prevented from entering the US. While the measure does not apply to government officials, Solana has withdrawn from his official duties since 2013.

“What they (the US) have is a computer with an algorithm, and if it knows you went to Iran recently, it takes you off the system,” he said.

“I’m going to try and make sure they let me go over. I need to go as I work there; I’m a professor in several universities.”