The top diplomat in China’s government arrived in Seoul on Wednesday, visiting South Korea for the first time in more than four years as the countries seek to repair ties that soured over the deployment of U.S. anti-missile systems in South Korea, Eurasia Diary reports citing Reuters.

During his two-day stay, State Councillor Wang Yi will meet South Korean Foreign Minister Kang Kyung-wha and President Moon Jae-in, officials in Seoul said.

Wang last visited the South Korean capital for a trilateral meeting, also attended by Japan, in 2015.

A year later a row blew up over the planned siting in South Korea of the U.S. Terminal High Altitude Area Defence (THAAD) system, designed to intercept ballistic missiles.

Beijing said it upset the regional security balance as the system’s powerful radar could penetrate into Chinese territory.

South Korea and the United States went ahead regardless, installing the anti-missile system in 2017, saying it was warranted because of North Korea’s provocations.

“The toughest time for bilateral relations has passed, but some problems caused by the deployment of the THAAD system in South Korea remain,” Cheng said.

North Korea has test fired dozens of missiles since Moon Jae-in took office in 2017, most recently on the U.S Thanksgiving holiday last week.

South Korea sees China as instrumental in reviving stalled denuclearisation talks between the United States and North Korea, a longtime ally of Beijing.

The agenda for Wang’s visit in Seoul is likely to include plans for a trilateral summit with Japan to be held in China later in December, a possible visit by Chinese President Xi Jinping to South Korea, as well as the stalled denuclearisation talks with North Korea, Yonhap news agency reported.

South Korea is seeking to open additional military hotlines with China to improve communications. The two countries’ defence ministers discussed the issue on the sidelines of an international conference in Bangkok last month, Seoul’s defence ministry said.