UNITED NATIONS—China will establish a 10-year, $1 billion “peace and development” fund to support the work of the United Nations, Chinese President Xi Jinping told the U.N. General Assembly on Monday in the opening session of its general debate.

China would join the new U.N. peacekeeping capability readiness system and take the lead in setting up a permanent peacekeeping police force and a standby force of 8,000 troops, President Xi said.

The Chinese government also would provide $100 million of free military assistance to the African Union in the next five years to support the establishment of an African standby force and enhance African crisis response capacity, Mr. Xi said.

Mr. Xi has sought to demonstrate leadership on the global stage and ease international concerns about China’s growing power by pledging billions of dollars in funding for international development at the tail end of his weeklong visit to the U.S.

The pledges appeared designed to portray China as a global leader on social issues following Mr. Xi’s summit with U.S. President Barack Obama on Friday that was dominated by tensions over Beijing’s economic policies, alleged cyberattacks on the U.S., and island-building in the disputed South China Sea.