The Trump administration has ordered US diplomatic missions to toughen screenings for visa applicants in "populations warranting increased scrutiny," diplomatic cables sent by Secretary of State Rex Tillerson reveal. US embassies have also been ordered to conduct "mandatory social media checks" for applicants who have ever been in territory controlled by the Islamic State (Isis).

The memos issued by Tillerson over the last two weeks are the first pieces of evidence of President Donald Trump's "extreme vetting". According to The New York Times, the new rules do not typically apply to citizens from 38 countries, including most of Europe and allies such as Australia, New Zealand, South Korea and Japan. Citizens of those country are admitted into the US under a visa waiver programme.

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Tillerson's directives provided instructions for implementing the president's revised travel ban, which temporarily barred visitors from six Muslim-majority countries and all refugees. The new executive order, which was issued on 6 March and was set to go into effect on 16 March, was temporarily blocked by a federal judge in Hawaii.

The cables, which were sent between 10 March and 17 March, instituted tougher rules for those who can enter the US while the administration works through the court system to unfreeze the latest executive order. According to Reuters, the final cable gave consular chiefs instructions to convene groups of law enforcement and intelligence officials to "develop a list of criteria identifying sets of post applicant populations warranting increased scrutiny."

The 17 March memo noted that applicants falling in one of the identified population groups should be considered for additional higher-level screenings. An early memo, sent 15 March, suggested areas of questioning during a required interview, including travel history, living and work history for the last 15 years, phone numbers and online accounts used in the last five years.

Trump has advocated for the "extreme vetting" of foreign visitors as a way to protect the country from a terrorist attack. "Consular officers should not hesitate to refuse any case presenting security concerns," Tillerson wrote in the cables. "All visa decisions are national security decisions."

Consular officials and immigration advocates, however, argue that the new rules will slow down the approval process and increase the probability of denial for visa seekers, The New York Times reported. Advocates also worry that people will be profiled for additional security screenings due to their name or nationality.

"Most posts already have populations that they look at for fraud and security issues," Jay Gairson, a Seattle-based immigration attorney, told Reuters. "What this language effectively does it give the consular posts permission to step away from the focused factors they have spent years developing and revising, and instead broaden the search to large groups based on gross factors such as nationality and religion."

Virginia Elliott, a spokeswoman for the State Department's Bureau of Consular Affairs told Reuters that the department was working to implement Trump's executive order "in accordance with its terms, in an orderly fashion, and in compliance with any relevant court orders, so as to increase the safety and security of the American people."