Police at three U.S. universities ordered mass evacuations Friday, after authorities received anonymous bomb threats. In one case, a caller told University of Texas-Austin officials that bombs had been place across the huge campus and that he belonged to al-Qaida.

Texas officials and police at North Dakota State University later deemed both campuses safe, and authorities were working late Friday to determine if the threats to the schools — more than 1,800 kilometers apart — were related. A third threat in northeastern Ohio also triggered an evacuation at Hiram College, where police with sniffer dogs remained on patrol Friday evening.

The threats came on a day of heightened anti-U.S. protests in North Africa and the Middle East, apparently spawned by an anti-Islam film said to have been produced in the United States.

But authorities have not connected the campus threats to the international unrest, which spread Friday to Sudan, Yemen, Tunisia and Indonesia.

An estimated 70,000 people were evacuated from the University of Texas campus and 20,000 others from the campus in Fargo, North Dakota. Some 1,300 people were evacuated from the much smaller Hiram College.