BRUSSELS — Javier Solana, a former secretary general of NATO who played a central role in negotiations over Iran’s nuclear program when he was the European Union’s foreign policy chief, has been denied electronic authorization to enter the United States because of a visit to Iran in 2013.

Mr. Solana said on Monday that his renewal application on the Electronic System for Travel Authorization, or ESTA — which determines the eligibility of visitors from certain countries to travel to the United States without having to apply for a visa — had been rejected for the first time. He said he would apply for a visa instead, a more cumbersome and expensive process.

Mr. Solana, 75, a Spanish citizen whose travel authorization problem was first reported by the daily El País, said that he considered it “to be more bureaucratic than political.”

In 2016, the Obama administration, responding to restrictions decided in Congress, tightened requirements to prevent citizens of 38 countries who had traveled to Iran, Iraq, Libya, Somalia, Sudan, Syria or Yemen after March 1, 2011, from coming to the United States under the online visa-waiver program. It also required visa applications of people from the 38 countries who were also citizens of Iran, Iraq, Sudan or Syria.