The head of the International Atomic Energy Agency says North Korea’s uranium enrichment facility has doubled in size in recent years, making it unlikely a diplomatic effort to curb its nuclear program will succeed, the Wall Street Journal reported Monday.

IAEA Director General Yukiya Amano, who helped negotiate the Iran nuclear deal, told the Journal the situation in North Korea is very different, and his agency is worried about the regime’s willingness to export its expertise.

“The situation is very different. Easy comparisons [to Iran] should be avoided,” he told the Journal.

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Secretary of State Rex Tillerson was in Asia in recent days, meeting with officials in South Korea, Japan and China, with North Korea high on the list of issues. He said in an interview with the Independent Journal Review U.S. patience with the North is running thin, and “all options are on the table.” Tillerson rebuffed a Chinese offer to set up direct talks with Kim Jong Un.

Amano said the North has ramped up plutonium production and uranium enrichment at its Yongbyon nuclear facility, doubling its size. North Korea expelled IAEA weapons inspectors in 2009 and has since conducted a number of underground nuclear tests and fired a series of ballistic missiles. IAEA has been monitoring the North’s progress through satellite imagery.

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The North tested a rocket engine Sunday, and the South Korean Defense Ministry said the engine performance showed progress, possibly an effort to develop a new engine, CNN reported. Pyongyang called the test a “great leap forward” for its rocket program.

“All of the indications point to the fact that North Korea is making progress, as they declared,” Amano said.

Amano refused to speculate on how many nuclear bombs the North has developed. U.S. and Chinese officials have said the number may be as high as 40.

North Korea has boasted it is developing a missile that could carry a nuclear warhead to the U.S. West Coast, but South Korea and Japan remain the most likely targets.

Presidents Bill Clinton, George W. Bush and Barack Obama all pursued diplomatic agreements with Pyongyang but the North cheated and backtracked on each pact.