North Korea threw next month’s summit between Kim Jong Un and U.S. President Donald Trump into doubt on Wednesday, threatening weeks of diplomatic progress by saying it may reconsider if Washington insists it unilaterally gives up its nuclear weapons.

The North’s official KCNA news agency said earlier Pyongyang had called off high-level talks with Seoul, which had been due on Wednesday, in the first sign of trouble after months of warming ties.

Citing first vice minister of foreign affairs Kim Kye Gwan, KCNA later said the fate of the unprecedented U.S.-North Korea summit, as well as bilateral relations, “would be clear” if the United States spoke of a “Libya-style” denuclearisation for the North.

“If the U.S. is trying to drive us into a corner to force our unilateral nuclear abandonment, we will no longer be interested in such dialogue and cannot but reconsider our proceeding to the DPRK-U.S. summit,” Kim Kye Gwan said, referring to the North by its official name, the Democratic People’s Republic of Korea.

Trump and Kim are scheduled to meet in Singapore on June 12.

The vice minister specifically criticized U.S. national security adviser John Bolton, who has called for North Korea to quickly give up its nuclear arsenal in a deal that mirrors Libya’s abandonment of its weapons of mass destruction.

North Korea clashed with Bolton when he worked under the Bush administration, calling him “human scum” and a “bloodsucker”.

“We shed light on the quality of Bolton already in the past, and we do not hide our feeling of repugnance towards him,” vice minister Kim said.