Japan will postpone a trilateral summit with China and South Korea due to Beijing's reluctance to take part, diplomatic sources said Thursday. The summit had previously been proposed for late July in Tokyo.

The move comes amid deteriorating relations between Beijing and Seoul over South Korea's deployment of a U.S. missile defense system designed to respond to a series of missile tests by North Korea.

China has strongly demanded that South Korea scrap the deployment of the Terminal High Altitude Area Defense system, believing that its radar lets the U.S. military spy on Chinese territory.

Japan now hopes to host the summit by the end of the year, as China is scheduled to hold a Communist Party Congress this fall — a gathering held once every five years at which many members of the party committee are expected to be replaced.

By hosting the summit, Prime Minister Shinzo Abe hopes to strengthen cooperation with his Chinese and South Korean counterparts to address threats from North Korea's nuclear and ballistic missile programs, while accelerating preparations for a visit to China he aims to arrange early next year, the sources said.

Tokyo had told Beijing and Seoul that it was considering hosting the summit sometime in late July, but China replied that participation would be "difficult," the sources said.

South Korea hosted the summit in 2015 and Tokyo is due to host the next one. A plan to hold one last year was dropped amid political turmoil in South Korea, but the nations held a foreign ministerial meeting in Tokyo in August 2016.

Summit-hosting duties have rotated since 2008, although the gatherings were not held in 2013 and 2014 after a chill in relations between Japan and China over a territorial row.