Scam artist. The guy calling, in very broken English, claimed to be from the FBI. He further claimed that they were giving me a chance to avoid prosecution for alleged tax evasion (presumably, if I called them back with my credit card number and identifying information). The call was from Washington State, but the numerous grammatical errors and heavy accent make me wonder where this [***] is really from.

Just your typical IRS scam calls, saying that you are being sued and need to call back to avoid legal action. Maybe someone should tell them that there is a Washington STATE, and they picked a wrong area code to spam with?

SCAM!!
India accent claiming to be from the FBI with an arrest warrant from the IRS.
I hung up at this point and blocked the number

This indian accent speaking man barely spoke English but repeated this number often.  I used to get calls from this number before and it stopped.  Now he is calling again.  Want it to stop again.  This is a spam call.  First off the message was cut off half way into message but long enough for his phone number to be given twice.