France's President Emmanuel Macron (right) and Norway's Prime Minister Jonas Gahr Store (left) shake hands after a ceremony at the Elysee Palace in Paris on Thursday. CHRISTOPHE PETIT TESSON VIA REUTERS

Norway will begin talks on joining a France-led nuclear deterrence program, the countries' leaders announced, a move that, if concluded, would be a notable shift for a traditionally Atlanticist nation long aligned with the United States on security.

France's President Emmanuel Macron and Norway's Prime Minister Jonas Gahr Store signed a mutual defense agreement during a meeting in Paris on Wednesday.

The deal would see Norway join what France describes as "forward nuclear deterrence", which is a framework that would involve European partners more closely in French strategic nuclear planning, Reuters reported.

The announcement comes amid widening European doubts about long-term US guarantees and efforts to build a more autonomous European defense posture, as even staunch US-oriented allies recalibrate.