From BBC News
27 January 2011 Last updated at 07:15 ET
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A US military base that carries out tests to protect troops against biological attacks was locked down on Wednesday to resolve a "serious concern", officials have said.
The base in Dugway, Utah, reopened early Thursday to allow staff in and out. There were reported to be 1,200 to 1,400 people inside Dugway at the time.
Base commander Col William King said on Wednesday no-one was in danger.
No information was given on the nature of the problem.
The primary mission for the base, which is located about 85 miles (135km) south-west of Salt Lake City, is defending troops against biological and chemical attacks.
"Measures like these are not taken lightly. No-one is in immediate danger, but these steps are required," Col King said.
