Since the first American shipments of sophisticated weapons to Ukraine, U.S. President Joe Biden has never wavered on one prohibition: Ukrainian President Volodymyr Zelenskyy had to agree to never fire them into Russian territory, with Washington insisting that doing so would violate Biden’s mandate to "avoid World War III.”

But the consensus around that policy is fraying. Propelled by the State Department, there is now a vigorous debate inside the administration over relaxing the ban to allow the Ukrainians to hit missile and artillery launch sites just over the border in Russia — targets Zelenskyy says have enabled Moscow’s recent territorial gains.

The proposal, pressed by U.S. Secretary of State Antony Blinken after a sobering visit to Kyiv, Ukraine, last week, is still in the formative stages, and it is not clear how many of his colleagues among Biden’s inner circle have signed on. It has not yet been formally presented to the president, who has traditionally been the most cautious, officials said.