The F.B.I. scolded several news outlets on Wednesday for mistakenly reporting that an arrest had been made in the Boston Marathon bombings, and warned that such unverified reporting could have “unintended consequences” for its investigation.

Numerous organizations, including The Associated Press, The Boston Globe and several local Boston television stations, erroneously reported Wednesday afternoon that an arrest had been made, or that a suspect was in custody, citing unnamed law enforcement sources. Two of the reports came from CNN and the Fox News Channel, both the subject of widespread criticism last June after misreporting the result of the Supreme Court ruling on President Obama’s health care overhaul law.

CNN and Fox News spent about an hour discussing the news of an arrest with various correspondents and experts before backing off when they received further information.

NBC News held back on reporting news of an arrest during continuing coverage on its MSNBC cable channel. It reported that no arrest had been made and that no person had been firmly identified as under suspicion. (The New York Times did not report that there was a suspect or an arrest.)