US President Donald Trump's temporary ban on refugees and travelers from six mainly Muslim countries came into effect late Thursday, after the Supreme Court allowed it following a five month battle with rights groups.

The Trump administration says the ban is necessary to block terrorists from entering the country, but immigrant advocates charge that it illegally singles out Muslims.

The 90-day ban on visitors from Iran, Libya, Somalia, Sudan, Syria and Yemen will allow exceptions for people with "close family relationships" in the United States, which the government has defined narrowly, excluding grandparents and grandchildren, aunts and uncles and others.