In a rare move, North Korea’s parliament sent a letter of protest to the U.S. House of Representatives on Friday over its new package of tougher sanctions.

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The Foreign Affairs Committee of North Korea’s Supreme People's Assembly condemned the sanctions as “the most heinous act against humanity” in the letter, according to a copy published by the KCNA news agency. 

The U.S. House voted overwhelmingly on May 4 to impose new sanctions on North Korea for advancing its nuclear and ballistic missile programs. It aimed at targeting the country's shipping industry and alleged use of slave labor. 

The Foreign Affairs Committee said these sanctions “run counter to the efforts aimed at ensuring peace and security on the Korean peninsula.”

Tensions in the region have intensified as Western powers continue to threaten North Korea for developing defensive nuclear and missile technology. The threats come as North Korea considers holding its sixth nuclear test and another ballistic missile launch.

North Korea warned in the letter that if the U.S. enacts more sanctions, it will strengthen its nuclear energy at “greater pace, beyond anyone’s imagination.”

“The U.S. House of Representatives should think twice,” the committee said in the letter.

As North Korea and the U.S. have no diplomatic relations and no official channels of communication, it is not clear how the letter was sent. But it’s rare to hear such direct protests from North Korea to the U.S. Congress. 

It’s also notable that the letter was sent by the Foreign Affairs Committee, which was abolished in the late 1990s and revived last month. Western analysts claim this is an attempt by the Kim Jong-un government to improve relations with other countries — South Korea and the U.S. in particular — amid its deepening isolation.

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The bipartisan House bill bars ships owned by North Korea or by countries that refuse to implement U.N. sanctions on Pyongyang from operating in U.S. waters or docking at U.S. ports. Goods produced by North Korean labor would be barred from entering the U.S. market under the bill.
 
It also requires President Donald Trump’s administration to determine within 90 days whether to include North Korea onto the government’s "state sponsors of terror" list along with Iran, Sudan and Syria. Such a designation would trigger more sanctions.

The U.S. Senate would need to approve the new sanctions next, before they could be signed into law.