Several federal agencies, including the FBI, conducted an operation Thursday morning in the Oakland, Calif., area, sources from the U.S. Attorney's Office told NBC News.

Among the registered residences is one belonging to Sheng Thao, mayor of Oakland. The Democratic leader's office said it was aware of the situation, but said it would let the FBI make a statement on the matter.

A neighbor interviewed by Politico contended that agents knocked on the mayor's door around 6 a.m. and that Thao was escorted out of her home.

Although the reason for the raid is unknown, anonymous sources said it was part of an investigation into the mayor.

Thao is the subject of criticism for the crime wave Oakland is facing. In November, she will face a recall vote.