PHOTO: REUTERSThe US has revoked more than 600 visas from foreign nationals in the last month as part of a major offensive against "birth tourism" rings, the State Department said on Wednesday. “American citizenship is not for sale,” Secretary Marco Rubio wrote on the US social media company X.American citizenship is not for sale. The State Department recently established the Birth Tourism Prevention Task Force to identify and dismantle the networks. “The State Department will use all available tools to dismantle birth tourism networks and defend the integrity of US citizenship,” Rubio said. Limiting birthright citizenship has been one of the top priorities in the Republican president's crackdown on immigration, with the ‌White House taking particular aim at what it calls "birth tourism," in which pregnant foreigners travel to the US to give birth.