WASHINGTON — U.S. President Donald Trump's administration on Thursday unveiled new visa rules that would limit foreign students and other nonimmigrants to fixed periods of stay, a move set to affect more than 13,000 Koreans currently in the United States under these categories. The U.S. Department of Homeland Security (DHS) issued the "final rule" to root out what it characterized as "visa abuse" by foreign students, exchange visitors and foreign journalists who exploit the system to extend their stay in America. The new rules will be published in the Federal Register on Friday and come into force 60 days after the publication, according to the DHS. "For decades, foreign students have been admitted into the U.S. indefinitely, allowing thousands to abuse our immigration system by perpetually enrolling in courses to avoid having to leave the U.S.," DHS Secretary Markwayne Mullin said in a release. "By implementing clear, finite limits on these visas, the United States is reclaiming its ability to properly screen, vet, and monitor individuals within our borders. This final rule ensures th