The United States is imposing new restrictions on the granting of tourist visas to pregnant foreign women travelling to the country, citing security concerns over so-called "birth tourism".

The new rules were unveiled by the State Department on Thursday, and seek to put an end to the practice of giving birth in the US so that the child can obtain US citizenship.

It is not clear how the State Department would determine that people seeking to travel to the US are pregnant, though the rule requires that officials reject visa applications when the individual's "primary purpose" is to obtain American citizenship for a child by giving birth on US soil.

"Closing this glaring immigration loophole will combat these endemic abuses and ultimately protect the United States from the national security risks created by this practice," White House press secretary Stephanie Grisham said in a statement, alleging that birth tourism overburdens hospital resources and that it is "rife with criminal activity".

She continued: "It will also defend American taxpayers from having their hard-earned dollars siphoned away to finance the direct and downstream costs associated with birth tourism. The integrity of American citizenship must be protected."

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The State Department does not keep official figures documenting the number of foreigners who travel to the United States specifically to give birth, though the department has said that it has received reports from embassies and consulates that there has been an increase in the practice recently.

The Centre for Immigration Studies, a conservative group that advocates for stricter immigration law, has meanwhile estimated that there were 33,000 births to women in the country who were visiting the country on temporary tourist visas in the second half of 2016 and first half of 2017.

"The final rule addresses concerns about the attendant risks of this activity to national security and law enforcement, including criminal activity associated with the birth tourism industry, as reflected in federal prosecutions of individuals and entities involved in that industry," the State Department said.