"The reason for lifting missile restrictions in Ukraine is the dispatch of North Korean troops."

U.S. President Joe Biden's decision to allow Ukraine to use long-range missiles was the dispatch of North Korean troops, Reuters reported on the 21st, citing an unnamed source.

Ukrainian President Volodymyr Zelensky has been asking for months to lift restrictions on the use of the U.S.-provided Atax missile so it can strike mainland Russia.

Biden continued to reject such requests, but he defied his insistence as a response was needed to Russia's move to deploy North Korean troops in Russia's Kursk region, Reuters said.

Reuters also noted that U.S. President-elect Donald Trump, who will take office two months later, has been negative about supporting Ukraine, and that the Biden administration's decision needs to be bolstered before that.

According to an anonymous source cited by Reuters, the U.S. decision to lift restrictions on the use of long-range missiles was delivered on a call between U.S. Defense Secretary Lloyd Austin and Ukrainian Defense Minister Rustem Umerow on the 12th.

The next day, U.S. Secretary of State Tony Blinken, who was in Brussels, informed Mark Rutter, NATO Secretary-General and European officials, and Ukrainian Foreign Minister Andriy Sibihar of the decision.

A senior U.S. government official explained to Reuters that the U.S. intention in the move was to send a message to North Korea and Russia that "we cannot allow North Korean troops to be sent," while blocking attempts by North Korea and Russia to drive out Ukrainian forces that have occupied parts of the Kursk region.

An aide to a federal lawmaker said he understood the lifting only applies to the Kursk region.