An agreement had been meant to be adopted following a plenary session earlier on Wednesday, but the source said it had been delayed after Indian Prime Minister Narendra Modi introduced new admission criteria.
Asked about the delay, an Indian official aware of the details of the talks told Reuters late on Wednesday that the discussion were continuing.
"Yesterday ... India pushed for consensus on criteria as well as the issue of (candidate) names. There was a broad understanding," he said.
The BRICS country official said that admission criteria India's Modi proposed included requiring members not be the target of international sanctions, ruling out potential candidates Iran and Venezuela.
Modi was also pushing for a minimum per capital GDP requirement.
"These are the things Modi brought in today," the official said. "So they are becoming a little bit of a spoiler."
Modi apparently played a last-minute spoiler role:
Looks like he ultimately conceded on Iran.