Jean-Claude Juncker, head of the European Union executive, said today he was not pushing for a "European super-state".
His comments appeared to be a rebuff to Brexit supporters who criticised him for seeking closer integration within the bloc.
The European Commission chief spoke as British Foreign Secretary Boris Johnson, in a Brexit policy speech in London, denounced Europe's attempts at ever-closer linkages of its member countries.
"Some in British political society are against the truth, pretending that I am a stupid, stubborn federalist, that I am in favour of an European super-state," Juncker told a news conference in Brussels.
"I am strictly against a European super-state. We are not the United States of America ... This is total nonsense," he stated.
His comments seemed a direct response to Johnson who said in London that Britain might stay aligned with some EU regulations after Brexit but is determined to leave the EU as its laws are meant to "to create an overarching European state."
"The process of integration has deepened and the corpus of EU law has grown ever vaster and intricate, and ever more powers and competencies have been handed to the EU institutions," Johnson said.
Since Britain's 2016 referendum ended with a narrow victory for the Leave over the Remain camp, the process of extricating the country from the bloc has proven more and more difficult.
The EU's chief Brexit negotiator last week warned London that the transition was not a done deal, pointing to what he called "substantial" differences in how the two sides imagine that period.
The bloc also wants Britain to explain what sort of future relationship it would pursue with the EU from 2021 if the two sides are to start talks on the matter.
Boris Johnson was kicking off a series of speeches by senior British cabinet ministers that Prime Minister Theresa May says will flesh out the "road to Brexit".