BEIJING(Yonhap)-- China, North Korea's foremost ally and its biggest trading partner, is trying "very hard" to exert its influence in persuading the North to abandon its nuclear weapons program, a former Chinese diplomat said Tuesday.

Ruan Zongze, now vice president of the China Institute of International Studies, said, however, that he expects no major policy changes toward North Korea by China's new leadership,despite Beijing's growing frustration with its unpredictable ally.

China's patience with North Korea has been wearing increasingly thin, particularly after the North's third nuclear test in February. Beijing voted in favor of sanctions by the U.N. Security Council to punish Pyongyang for conducting the nuclear test.

In May, the Bank of China closed accounts with North Korea's Foreign Trade Bank, which was accused by the U.S. of helping finance the North's nuclear weapons program.

 "In handling relations with the DPRK (North Korea), China is trying very hard to exert its own influence," Ruan told reporters at a forum hosted by the All-China Journalists Association.

 Ruan noted China's policy of persuading North Korea to end its nuclear program through dialogue.

 "Recently, there is a misunderstanding, and some people say China is no longer insisting on denuclearization, and China will place peace and stability before denuclearization," Ruan said. "I don't agree with that. Denuclearization and peace and stability are two sides of one coin," he said.

Asked about a possible policy change by China's new leadership towards the North, Ruan replied, "I don't think that there will be a major change."

After months of simmering tensions triggered by its third nuclear test in February and bellicose threats against South Korea and the United States, North Korea has recently appeared to have shifted to a charm offensive, offering talks with them.

Seoul, Washington and Tokyo, however, have called on Pyongyang to first demonstrate its sincerity for denuclearization through actions before such talks take place.

South Korea and the U.S. are set to launch their annual joint military drills this month, with North Korea warning that the Korean Peninsula would plunge into a "state of catastrophe" if Seoul and Washington move forward with the drills.