Updated

A new study of homegrown terrorism in the United States says that the threat of radicalization among American Muslims has been overstated.

Researchers identified 139 American Muslims who had been accused of planning or carrying out terror-related violence since the September 11 attacks.

The report's authors say that number is significant but small compared to terror cases in other countries, and compared to overall violent crime in the U.S.

The study credits self-policing in American Muslim communities for limiting radicalization.

The report released Wednesday is from Duke University and the University of North Carolina in Chapel Hill. There was a spike in the number of cases last year, but researchers say it's too soon to know whether that's a trend.