Ukraine will not amend its Constitution as part of any potential peace deal, Interfax-Ukraine reported Wednesday, citing a member of the Ukrainian delegation involved in talks with the United States, other partners and Russia.

"We have stated that Ukraine will not accept any form of recognition and Ukraine will not make any changes to the Constitution -- these are red lines," said Oleksandr Bevz, an adviser to the head of Ukraine's presidential office.

He said territorial issues should be addressed on two principles: the current contact line should serve as the basis for talks, and such questions must be handled at the level of national leaders.

According to head of the presidential office Andriy Yermak, Ukrainian and U.S. negotiators have reached agreement in principle on most elements of Washington's proposed peace plan, though it has been significantly revised from the original 28 points.

On Tuesday, President Volodymyr Zelensky said the updated plan could evolve into "deeper agreements."