DUBAI — Talks on a proposed treaty governing international telecommunications collapsed in acrimony on Thursday when the United States rejected the agreement on the eve of its scheduled signing, citing an inability to resolve an impasse over the Internet.

“It is with a heavy heart that I have to announce that the United States must communicate that it is unable to sign the agreement in its current form,” Terry Kramer, head of the American delegation, announced moments after a final draft appeared to have been approved by a majority of nations.

The United States announcement was seconded by Canada and several European countries after nearly two weeks of talks that had often pitted Western governments against Russia, China and developing countries. The East-West and North-South divisions harked back to the cold war, even though that conflict did not stop previous agreements to connect telephone calls across the Iron Curtain.

While the proposed agreement was not set to take effect until 2015 and was not legally binding, Mr. Kramer insisted that the United States and its supporters had headed off a significant threat to the “open Internet.”