The anniversary Thursday of a 1931 incident that led to Japan’s occupation of northeastern China was marked by tight security as the two countries struggle to improve relations strained in recent years over a territorial dispute and historical issues.

A ceremony to mark the 83rd anniversary of the Mukden Incident, also called the Manchurian Incident, took place at a history museum in Shenyang, with Liu Yunshan, the Chinese Communist Party’s fifth-ranked leader, delivering a speech saying that remembering a “national disgrace” will help secure a brighter future.

A large number of security officials were deployed near the 9.18 Historical Museum in the early morning, while local authorities requested that Japanese restaurants in the city, called Mukden at the time of the incident, close their doors for the day.

On Sept. 18, 1931, Japanese military officers attempted to blow up a portion of a Japanese railroad north of the city and blamed it on Chinese dissidents. The incident is widely seen as the pretext for Japan’s invasion of northeastern China and the start of World War II for Japan.

During the anniversary two years ago, massive anti-Japan demonstrations were held in Shenyang and at least 124 other Chinese cities. The protests focused on Japan’s purchase a week earlier of the Senkaku Islands from a private owner in Saitama. The islets off Taiwan are claimed by China, which calls them Diaoyu, and Taiwan, which calls them Tiaoyutai.

Two of the three countries have failed to ease tensions heightened by Japan’s move, and by Prime Minister Shinzo Abe’s visit late last year to war-linked Yasukuni Shrine in Tokyo.

Taipei was mollified by a fishing pact with Japan.

Abe and Chinese President Xi Jinping have not held a summit since Abe came to power in December 2012.