BEIJING — The tensions were already high.

At a major international gathering in Papua New Guinea over the weekend, the United States wanted to end with a group statement emphasizing free trade. China objected.

But instead of working out the disagreement through dialogue, Chinese officials barged uninvited into the office of the host country’s foreign minister demanding changes in the official communiqué.

China’s action marked a striking break with diplomatic decorum at a meeting that is normally used to promote cooperation among countries that ring the Pacific Ocean.

The dispute meant that the Asia-Pacific Economic Cooperation, or APEC, forum held in Papua New Guinea and attended by Vice President Mike Pence and China’s leader, Xi Jinping, failed to issue a joint document for the first time since 1989.