Research that could make flu viruses more dangerous, and that the government suspended i n 2014 because of safety concerns, has been approved to begin again, federal officials have confirmed.

The government did not publicly announce its decisions in recent months to allow two labs to resume their projects. The new go-ahead was first reported in the journal Science.

The lack of information about the decision and how it was made have provoked outrage from some scientists, who oppose the research because they say it could create mutant viruses that might cause deadly pandemics if they were unleashed by lab accidents or terrorism. The research sparked worldwide fears when it was first revealed in 2011.

Two research teams, in Wisconsin and the Netherlands, have been told by the Department of Health and Human Services that their work is eligible for research funding from the United States government. The Wisconsin group was notified in October, and the Dutch group in January, a spokeswoman for H.H.S. said in an email.