DUBAI, United Arab Emirates — In a moment of high drama at the end of nearly two weeks of talks on an international telecommunications treaty, the United States rejected a proposal negotiated by more than 190 countries on Thursday after delegates were unable 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 US delegation, said moments after a final draft had been approved by a majority of nations.