North Korean leader Kim Jong Un's bromance with U.S. President Donald Trump may be on its last legs, as an end-of-year deadline set by Kim for progress fast approaches.

One of the North's former top nuclear envoys said in a statement Monday that Pyongyang was no longer interested in holding another summit with the U.S. if the North did not receive anything in return.

The statement by Kim Kye Gwan, who currently serves as a top adviser to the North Korean Foreign Ministry, came after Trump used a tweet Sunday to urge Kim Jong Un to "act quickly" to reach a nuclear deal with the United States. Trump's tweet, which was addressed to "Mr. Chairman" and included the sign-off "See you soon!" was widely seen as an entreaty for a third summit with Kim Jong Un.