March 1 (Reuters) - North Korea proposed to close down a portion of its Yongbyon nuclear complex in exchange for lifting of all U.N. sanctions except those directly targeting their weapons of mass destruction program, a senior U.S. State Department official said.

“The dilemma that we were confronted with is the North Koreans at this point are unwilling to impose a complete freeze on their weapons of mass destruction programs,” the official told reporters.

“So to give many, many billions of dollars in sanctions relief would in effect put us in a position of subsidizing the ongoing development of weapons of mass destruction in North Korea,” the official said.

The official spoke to reporters following the collapse of a second summit between U.S. President Donald Trump and North Korean leader Kim Jong Un in Vietnam on Thursday. (Reporting by Eric Beech in Washington; Editing by Mohammad Zargham)