The five-nation BRICS club of emerging economies that came together to tilt the international order away from the West announced plans Thursday to expand its membership, feeding concerns about a growing global divide.

The group said that Argentina, Egypt, Ethiopia, Iran, the United Arab Emirates and Saudi Arabia had been invited to join, and that their membership would begin in January.

The BRICS group, which encompasses Brazil, Russia, India, China and South Africa, announced the expansion at a summit in South Africa that attracted a level of global interest rarely seen in recent years. The group represents a quarter of the world’s economy and about 40 percent of the world’s population and has increasingly sought to be a counterweight to the dominance of Western-led forums like the Group of 7 and the World Bank.

Despite a public show of unity at the tightly controlled conference, the BRICS members brought divergent views on expansion. Several leaders warned against a return to a divisive global order reminiscent of the Cold War. India, which has been locked in a territorial dispute with China, has sought to avoid diluting its own role in the group in favor of countries closer to China. Brazil and South Africa have wanted to avoid alienating partners in Europe and North America.

The decision to bring Iran into the fold signals that Russia and China effectively pressured for its inclusion, said Cobus van Staden, a researcher with the China Global South Project.

“Iran, obviously, is a complicated choice,” said Mr. van Staden. “I can imagine that some of the other members worry that it might increase geopolitical tensions with Western powers, which I think it kind of inevitably would.”

The BRICS group has said that it wants to bring diversity amid increasing polarization. That polarization has been deepened by Russia’s invasion of Ukraine and strained relations on economic and security issues between the United States and China. Smaller countries caught between the world’s wealthier nations have faced pressure to pick sides or, in some cases, occupy a middle ground in an effort to get the best deal from the competing nations.

American officials have sought to play down the impact of the group’s expansion plans. On Tuesday, Jake Sullivan, the White House national security adviser, told reporters that the Biden administration is “not looking at the BRICS as evolving into some kind of geopolitical rival to the United States or anyone else.”

He said that the United States had “strong positive” relations with Brazil, India and South Africa, adding that “we will continue to manage our relationship with China; and we will continue to push back on Russia’s aggression.”

China’s leader, Xi Jinping, who had pushed for a rapid expansion of the group as his country has sought to pitch itself as a leader of the developing world, said the move to bring in new members was “historic.” Mr. Xi, in a speech read by a subordinate at the summit earlier this week, had said: “International rules must be written and upheld jointly by all countries, rather than dictated by those with the strongest muscles.”

Prime Minister Narendra Modi of India said on Thursday that the expansion of the group was “a message that all institutions in the world need to mold themselves according to changing times.”

Some of the countries that were invited to join have considerable practice walking a fine diplomatic line with the West. Saudi Arabia, the BRICS club’s biggest trading partner in the Middle East, has cultivated ties with China and has demonstrated independence from American interests despite its longstanding security relationship with the United States.

Egypt, politically and geographically straddling Africa and the Middle East, has built strong relationships with Russia and China, while maintaining its ties to the United States.

For Argentina, facing yet another economic crisis and diminishing foreign reserves, membership in the BRICS could be a financial lifeline. During the summit, Mr. Lula has championed the creation of an alternative trading unit that would ease emerging nations’ dependence on the strong U.S. dollar. Argentina has already begun repaying some of its loans in the Chinese currency, analysts said, though it is unclear how much relief it will gain.

Iran applied to join BRICS in June as part of its efforts to strengthen economic and political ties with non-Western powers and to demonstrate that the West’s efforts to isolate the country have failed. The country, which holds the world’s second-largest gas reserves and a quarter of the oil reserves in the Middle East, has stayed afloat by selling discounted oil to China, among other maneuvers.

The United Arab Emirates, which was also invited as a formal member, had already joined the BRICS’ New Development Bank in June.

David Pierson contributed reporting from Hong Kong, Edward Wong from Washington, and Isabella Kwai from London.