BEIJING - China's President Xi Jinping expressed his condolences on Saturday over the death of former Japanese Prime Minister Shinzo Abe, whom Xi said had worked hard to improve relations between the neighbours, Chinese state media reported.

Japan's longest serving modern leader was gunned down on Friday in the Japanese city of Nara while making a campaign speech for a parliamentary election. A 41-year-old Japanese male suspect has been arrested.

"I deeply regret his sudden death," state media quoted Xi as saying on behalf of the Chinese government and people in a message to Japanese Prime Minister Fumio Kishida.

"I once reached important consensus with him on building China-Japan relations."

Xi also extended his condolences to Abe's family, state television reported.

Ties between Japan and China have been plagued for years by a territorial dispute over a group of tiny East China Sea islets as well as the legacy of Japan's past military aggression.

But relations warmed while Abe's was prime minister, particularly during his second term from 2012 to 2020.

Abe made a rare state visit to China in 2018 and, in return, Xi was expected to visit Japan in 2020, which would have marked the first trip by a Chinese president to Japan since 2008.

But the plan was shelved because of the COVID-19 outbreak.

Bilateral ties have become more complex in recent months, with Kishida's government calling for increased defence spending and expressing concern over threats faced by self-ruled Taiwan, which China claims as its own.

Kishida has also said he was disappointed by efforts by China to develop areas in the East China Sea, saying it was "unacceptable".

The dispute over the East China Sea islands, which Japan controls but China also claims, and the waters around them, has been a longtime source of tension between the world's second- and third-biggest economies.

In his message to Kishida, Xi said he was willing to work with him on developing friendly and neighbourly ties.

(Reporting by Ryan Woo and Tina Qiao; Editing by Robert Birsel)