A North Korean parliamentary committee on Friday sent a rare letter of protest to the U.S. House of Representatives, complaining about a proposed new package of tougher sanctions.
The sanctions were condemned as a "heinous act against humanity" by the foreign affairs committee of the North's Supreme People's Assembly, according to a state media report.
It's unclear how it was sent since North Korea and the United States don't have official channels of communication.
The report, carried by the North's Korean Central News Agency, said the letter was sent Friday.
The Republican-led House overwhelmingly voted May 4 to impose the new sanctions, which target North Korea's shipping industry and use of what the bill called "slave labor."
The bill bars ships owned by North Korea or by countries that refuse to comply with U.N. resolutions against it from operating in American waters or docking at U.S. ports.
Goods produced by North Korea's forced labor would be prohibited from entering the United States, according to the legislation.
The Senate would also need to approve the new sanctions before they could be implemented.
It's not unusual for Pyongyang to condemn Washington's moves to censure it, but direct protests to Congress are exceptionally rare.
The North also announced last week that it thwarted what it claims was a CIA-backed attempt to assassinate Kim. On Friday, its Central Public Prosecutor's Office issued a statement suggesting that the United States and South Korea are harboring suspects and should extradite them to the North immediately.
--The Associated Press contributed to this report.