BUDAPEST, Hungary (AP) — The United States imposed new travel restrictions on citizens of Hungary on Tuesday over concerns that the identities of nearly 1 million foreigners granted Hungarian passports over nine years were not sufficiently verified, according to the U.S. Embassy and a government official.

The restrictions apply to the U.S. Visa Waiver Program, which allows passport holders from 40 countries to enter the United States for business or tourism without a visa for up to 90 days.

The validity period of travel for Hungarian passport holders under the Electronic System for Travel Authorization was reduced from two years to one year, and each traveler will be limited to a single entry into the United States. They are the only such restrictions among the 40 participating states in the Visa Waiver Program.

A senior U.S. government official said the change followed years of failed efforts by the U.S. to work with Hungary’s government to resolve the security concerns. The official spoke anonymously in order to candidly characterize diplomatic engagements.

Hundreds of thousands of Hungarian passports were issued without stringent identity verification requirements, some of them to criminals who pose a safety threat and have no connection to Hungary, the official said.

Hungary’s government, under the leadership of Prime Minister Viktor Orban, began offering a simplified naturalization procedure to those claiming Hungarian ancestry in 2011, even if they did not live or intend to live in Hungary.

Hundreds of thousands of the at least 2 million ethnic Hungarians living in neighboring countries — primarily in Romania, Serbia and Ukraine — acquired Hungarian citizenship through the simplified procedure.

Critics said the program allowed non-taxpaying ethnic Hungarians residing in other countries to vote in Hungarian elections, giving Orban’s ruling Fidesz party an electoral edge.

The United States earlier recategorized Hungary as a provisional member of the Visa Waiver Program due to the concerns.