The rapprochement between Japanese Prime Minister Shinzo Abe and Chinese President Xi Jinping led to some candid exchanges during the two leaders' meetings on Friday, including some strong words of discontent from Xi toward U.S. President Donald Trump's trade pressure.

"Congratulations on your re-election as party leader," Xi told Abe as the two sat down for dinner at Beijing's Diaoyutai State Guesthouse on Friday evening. They had already concluded their 80-minute official summit, and the mood was relaxed.

Abe's September victory over party rival Shigeru Ishiba not only gave him a third term as president of the ruling Liberal Democratic Party, but also a chance to become Japan's longest-serving prime minister.

"You know, the Chinese Communist Party has 90 million members," Xi added.

"Is that so?" replied Abe, explaining that the LDP has about 1 million. The friendly exchange would have been unthinkable several years ago, when relations were said to have sunk to their worst since the two countries normalized diplomatic ties in 1972, over tensions over the East China Sea.

When the conversation shifted to the Sino-American trade spat, however, Xi's expression turned grim. "I'm against a unipolar system led by the U.S.," he said.

Xi expressed deep frustration with Washington's strong-arm tactics in trade negotiations. The free trade system should be respected, he told Abe.