U.N. climate talks have hit a stumbling block that some delegates say poses a serious challenge to their already slow-moving effort to craft a global response to climate change.

As the latest negotiation session ended Friday in the German city of Bonn, one track of the talks was paralyzed by a request by Russia, Ukraine and Belarus to review the decision-making procedure in the two-decade-long U.N. process.

Seychelles delegate Ronald Jumeau said, "If we're not careful, it could collapse the whole system."

Decisions are supposed to be taken by consensus, but it's not clear what that means in practice. At several conferences, decisions have been "gaveled through" despite the objections of individual countries. That happened to Russia at last year's climate conference in Qatar.