In the aftermath of the terrorist attacks in California and Paris, the Obama administration on Thursday tightened a program that allows nationals of certain countries to travel to the US without a visa by restricting entry for those who have dual citizenship in Iran, Iraq, Sudan or Syria.

The Wall Street Journal said that under the program, nationals from 38 countries, primarily in Europe, may enter the US for tourism or business without a visa. Nationals of these countries who also are citizens of the four predominantly Muslim nations will no longer be eligible to gain automatic admission to the US, according to a joint statement by the State Department and the Department of Homeland Security.

In addition, those who don’t hold dual nationality but have visited those four countries on or after March 2011 no longer will be eligible for visa-free entry, the statement said.

People in both categories must "apply for a visa using the regular immigration process at our embassies or consulates," the statement said. That means they will undergo vetting and an interview with a US consular official overseas.

Nationals of visa-waiver-program countries must file an electronic form—with biographic, citizenship, travel and other information—to determine eligibility to travel to the US and whether such travel poses a law-enforcement or security risk.