Officials at the University of Texas and at North Dakota State University have ordered full campus evacuations after receiving bomb threats.
In a statement, University of Texas authorities said a threat was received from a man "with a Middle Eastern accent" at 08:35 (13:35 GMT).
He said he was with al-Qaeda and bombs were set to detonate 90 minutes later, according to the statement.
The University of Texas, Austin, is a sprawling campus in the city centre.
University spokeswoman Rhonda Wheldon told the Associated Press news agency all university buildings were evacuated at 09:50 as a precaution.
"Evacuation due to threats on campus. Immediately evacuate ALL buildings and get as far away as possible. More information to come," the evacuation order said.
No bombs have been found, Ms Wheldon added.
A later update at 10:46 noted the time specified in the threat had passed but that officials had not yet cleared all buildings. The decision whether to resume classes "will come shortly", the university said.
Shortly after the University of Texas issued its alert, North Dakota State University issued a similar notice, also saying it had received a bomb threat.
"NDSU is requiring all employees and students to leave campus by 10:15," theuniversity said.
"This includes residence hall students, who, if necessary, should walk to locations off campus. This also includes the downtown buildings and agricultural facilities."
There has been no update on that situation.----
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