The US has tightened a visa waiver programme for Hungarians after saying Budapest failed to ensure adequate identity checks for nearly 1mn people to whom it has granted citizenship in recent years.

The decision, announced by the US embassy in the Hungarian capital on Tuesday, is effective immediately. Under the new rules, the US’s Esta visa-waiver entry permit for Hungarian passport holders will be valid for one year rather than two and only allow single rather than multiple entry, the embassy said. The new rules do not affect approvals granted before the announcement.

In a statement, the embassy cited “security vulnerabilities created by [Hungary’s] earlier implementation of its simplified naturalisation process” for ethnic Hungarians in the region.