WASHINGTON--In a rare tie-up between the United States and China, both are increasingly sharing information regarding North Korea that includes whether Beijing is implementing economic sanctions as well as communication between their militaries, particularly in the region closest to North Korea.

Several U.S. government sources said an agreement was reached in early November when visiting U.S. President Donald Trump met with Chinese President Xi Jinping in Beijing.

According to those sources, Trump and Xi talked for about an hour and a half on Nov. 9 with only close associates in attendance. Much of the discussion centered on North Korea.

In the meeting, Xi confirmed that North Korea would not be allowed to possess nuclear weapons; that pressure would continue to be applied on Pyongyang until it abandoned its nuclear arsenal; and that transparency regarding economic sanctions and other measures applied to North Korea would be heightened.

Xi told Trump that China would agree to strengthen economic sanctions adopted by the U.N. Security Council and that Beijing would implement those sanctions in full.

As one way to heighten transparency on the sanctions imposed by China, reports would be submitted to U.S. officials from Chinese officials in charge of trade, customs and finance every few weeks or months regarding what China has implemented in relation to North Korea.

The latest U.N. Security Council resolution on Dec. 22 gained Chinese approval for limiting supplies of petroleum to North Korea should it conduct any further military provocations.

A diplomatic source said Chinese agreement on the tougher sanctions was the result of discussions between the governments of China and the United States.

Intelligence on North Korea's nuclear weapons and ballistic missile development programs will also be shared by the militaries and intelligence agencies of the two nations. The two sides will also share intelligence on the effects the sanctions have on North Korea's economy.

Sources said the intelligence sharing would extend to such issues as how to secure North Korea's nuclear weapons and dealing with refugees from North Korea should a military encounter occur with North Korea or if the regime of North Korean leader Kim Jong Un collapsed.

In addition to periodic meetings between high-ranking officials of the two nations' militaries and intelligence agencies, a direct hotline will be installed between the Seoul headquarters of U.S. forces based in South Korea and the Chinese military's Northern Theater Command, which is based in Shenyang, Liaoning province.

That command would be in charge of dealing with any military contingency in North Korea.

Sources said that U.S. officials indicated a more cautious approach would be taken concerning unilateral military action by the United States against North Korea as long as China continued to take a cooperative stance. U.S. officials also expressed understanding Beijing's policy of resolving issues regarding North Korea through dialogue.

At the same time, the cooperative relationship between the United States and China would depend on sufficient implementation of sanctions against North Korea and the sharing of intelligence.

”China is a major strategic competitor with the United States, I'm guessing that it probably was not the degree of actual detail of what we would consider in contingency planning that we would need to inform military operations,” said Oriana Skylar Mastro, Georgetown University assistant professor of security studies.