Washington, Jan 22 (IANS): The United States started implementing changes to the US Visa Waiver Programme (VWP) for citizens of 38 foreign countries.

Starting from Thursday, nationals of the VWP partner countries are required to get a visa ahead of their trip to the US if they "have travelled to or been present in Iran, Iraq, Sudan, or Syria on or after March 1, 2011," said a statement by the US state department.

Limited exceptions exist for travel for diplomatic or military purposes in the service of a VWP country, Xinhua reported.

In addition, nationals of VWP countries who are also nationals of the above mentioned four countries are no longer eligible for the VWP programme.

Despite the new restrictions, the US secretary of homeland security may still "waive these restrictions" on a "case-by-case basis" for individuals who travelled to the four countries as journalists, or on behalf of humanitarian agencies on official duty, or on behalf of international organisations, regional organisations and provincial or local governments, or for legitimate business-related purposes, according to the statement.

The VWP currently permits visa free travel for 20 million visitors each year to the US for citizens of 38 programme partner countries.

After the Paris terrorist attacks on November 13, 2015, which killed at least 130 people and injured over 300 others, US lawmakers and government officials worried that the current VWP, which allows citizens from partner countries to enter the US for as long as 90 days without a visa, could pose a security threat to homeland security.