During their first summit in June, South Korean President Park Geun-hye and her Chinese counterpart Xi Jinping agreed to make the waters between the two countries a “sea of peace, cooperation and friendship.” In the wake of the top leaders’ meeting, Seoul officials expressed hope Beijing would strengthen crackdowns on illegal fishing by Chinese vessels in South Korean waters.

After a lull over the past few months, however, Chinese boats are coming in flocks again to catch fish in South Korea’s exclusive economic zone in the Yellow Sea, clashing with the Coast Guard personnel who are trying to stop them. Four members of the South Korean Coast Guard were seriously wounded Monday while attempting to arrest 14 Chinese fishermen aboard a 120-ton boat that was operating in the waters near the southwestern island of Gageo. The Chinese fishermen brandished knives and metal pipes and hurled stones and bottles at the approaching officers. Two of them were also injured during the fight.

It is aggravating and worrisome to see Chinese fishing vessels going ahead with illegal operations and violently resisting South Korean Coast Guard officers in disregard of an agreement made by the leaders of the two countries just months ago.

Under a bilateral fisheries accord, South Korea and China are supposed to allow a total of 1,600 vessels from each other’s country to catch 60,000 tons of fish in their EEZ every year. With fishing grounds off China’s coast increasingly polluted, more than 200,000 Chinese boats have entered South Korean waters annually in recent years, prompting concerns that they are drying up marine resources and destroying the ecosystem in the Yellow Sea.

The recurrence of violent clashes between Chinese fishermen and South Korean officers has also exacerbated public sentiment on both sides. Public outrage erupted here in 2011 over the killing of a coast guard officer by a Chinese skipper during a fight for control of a trawler illegally fishing in South Korean waters. On the contrary, a Chinese fisherman’s death prompted protest from Beijing last year.

A day after the latest clash, South Korea expressed its regret to China through a diplomatic channel, calling on Beijing to come up with measures to prevent such incidents from recurring. The Chinese Embassy here was quoted by a Seoul official as promising to convey the message back to Beijing.

The two sides should move quickly beyond the diplomatic rhetoric to take more effective and thorough measures to crack down on illegal operations by Chinese fishing vessels.

China must turn its words on creating a sea of peace, cooperation and friendship into action. It does not fit the caliber of a superpower seeking to assume a leading role on the global stage to let its people repeatedly commit illicit acts in violation of a neighboring country’s sovereign rights.

South Korea, for its part, needs to respond more sternly, making Chinese fishermen pay a dear price for their illegal operations and violence. It may be useful to let Chinese officials board its patrol ships to witness in person the violent clashes.

Since taking the helm of their countries early this year, Park and Xi have held a string of meetings under an amicable atmosphere, the third and latest one last week on the sidelines of an Asia-Pacific Economic Cooperation summit on Indonesia’s resort island of Bali. It is certainly important for the two leaders to share understanding and pledge cooperation on broad strategic issues, including North Korea’s nuclear programs. But their commitment to deepening the bilateral partnership will lose some luster if their governments fail to prevent the recurrence of violent clashes in the waters envisioned as a peaceful sea.