People with dual nationalities are among those who will be affected by Donald Trump's ban on entry to the country for people from seven majority-Muslim countries.

The US president signed an executive order on 27 January, putting an indefinite ban on Syrian refugees and a 90-day visa ban on people from Iraq, Iran, Somalia, Sudan, Libya and Yemen – and also on people who hold dual nationality in one of the seven banned countries.

Brits holding both a British and Iranian passport, for example, will also be subject to the 90-day visa ban, according to a statement seen by The Wall Street Journal.

"Travellers who have nationality or dual nationality of one of these countries will not be permitted for 90 days to enter the United States or be issued an immigrant or non-immigrant visa," the statement read.

"Those nationals or dual nationals holding valid immigrant or non-immigrant visas will not be permitted to enter the United States during this period. Visa interviews will generally not be scheduled for nationals of these countries during this period."

US green card holders will also be affected by the ban - meaning at least 500,000 people who are legal permanent residents in the US could face problems if they have travelled abroad and are attempting to re-enter the US.

However, people holding dual nationalities with one of the seven countries and the US will not be affected by the ban, which has already led to the detention of 12 people at JFK Airport in New York.

Following Trump's announcement of the ban, Iran – one of the seven countries named in the executive order – has announced its own ban on US citizens.

"While respecting the American people and distinguishing between them and the hostile policies of the U.S. government, Iran will implement the principle of reciprocity until the offensive U.S. limitations against Iranian nationals are lifted," Iran's Foreign Ministry said in a statement.

"The restrictions against travel by Muslims to America ... are an open affront against the Muslim world and the Iranian nation in particular and will be known as a great gift to extremists," it added.