"We are contending with the most serious security situation since the Second World War," Norway's Prime Minister Jonas Gahr Store said as he and French President Emmanuel Macron announced in Paris that the two countries had signed a defence pact.

"In the past six months, we have entered into defence agreements with both Germany and the UK, and I am pleased that we have signed a comprehensive defence agreement with France today," he said.

In March, Macron unveiled a programme under which France, the European Union's only nuclear-armed country, would use its atomic stockpile to boost security on the continent.

Under the so-called "forward" nuclear deterrence scheme, those who join will be able to temporarily host French "strategic air forces", which will be able to "spread out across the European continent" to "complicate the calculations of our adversaries", Macron said at the time.

"Norway, a key geographical and strategic partner with which we already had significant cooperation in ensuring the protection of Allied territory against external threats, will represent a strong added value for this enhanced deterrence," Macron said.

Prior to Norway, eight countries had joined the programme -- Belgium, Denmark, Germany, Greece, the Netherlands, Poland, Sweden and fellow nuclear power the United Kingdom.

"The agreement reinforces our cooperation through concrete structures, plans, exercises and prepositioning of equipment, and will enable us to mount a swift and coordinated response when it is really needed," Store said.

"The agreement also provides a framework for closer cooperation on hybrid warfare, maritime security, space cooperation, cybersecurity, support to Ukraine and defence industrial cooperation."