The United States on Thursday began enforcing new visa rules on some travelers who have visited or who have dual nationality with states considered seedbeds of terrorism.
The Department of Homeland Security said would-be US visitors who have been to Iran, Iraq, Sudan or Syria since March 2011 will now always have to apply for a visa.
This will be the case even if the traveler is from a country in the US visa waiver program – the 40 nations seen as friends of America whose citizens can visit freely.
In addition, citizens of visa waiver countries who hold dual Iranian, Iraqi, Sudanese or Syrian nationality will have to apply for a full visa before traveling to the US.
The department said it had started to implement the new rules on Thursday, but there had already been reports of travelers falling afoul of the controversial regulations.
On Wednesday, the BBC reported that its journalist Rana Rahimpour, who has joint British and Iranian nationality, had been kept from boarding a US-bound flight.
The State Department refused to comment on specific cases.
"We will carry out the law that Congress passed and the president signed," a senior administration official told AFP, speaking on condition of anonymity.
"The Department of Homeland Security… is working closely with the Department of State and other partners to ensure that the new amendments… are appropriately implemented."
Homeland Security said dual nationals and travelers who had visited the four targeted countries would still be eligible for visas if they apply for them properly.
But they will no longer be able to skip the visa process by registering with the Electronic System for Travel Authorizations like fellow waiver country citizens.
Members of allied forces who fought alongside US troops in Iraq will be exempted from the new rules, and aid workers and journalists may be exempted on a "case-by-case" basis.