According to Finland's former president Sauli Niinistö, no-one could have predicted that the alliance's main member would threaten to invade the territory of another Nato country.
He was referring to US President Donald Trump's repeated statements that the US should annex Greenland, one way or the other.
Niinistö, who left office after two terms and oversaw Finland joining Nato, made the comments to Finnish commercial broadcaster MTV.
On Wednesday, Danish and Greenlandic officials visited Trump in the White House, in an effort to thwart the administration's stated plans. After the meeting, Trump reiterated that the US needs Greenland. The American president has on several occasions said that he has not ruled out military action in achieving that goal.
According to Niinistö, even if the US does decide to move forward with an aggressive policy regarding Greenland, it cannot mean the end of Nato.
"Let’s take Nato into European hands, or try to buy time in the hope that something will change in the United States," he told MTV.
According to Niinistö, if the US were to attack Greenland, the EU's mutual assistance clause, Article 42.7 of the Lisbon Treaty, could also be put to the test.
Niinistö leads work on joint European defence report
Niinistö is leading joint work on a report about how Europe can guarantee its own defence without the participation of the United States, according to newspaper Iltalehti.
Niinistö is chairing the working group behind the report, which will be published by the Brussels-based think tank, the Centre for European Policy Studies (CEPS).
Once the report is complete, likely in March, it will raise the issue of Europe establishing a joint military. Several high-level experts from different countries are involved in the work.
According to Niinistö, the report is urgently needed. The former president said he hopes that European countries will take the report's recommendations very seriously.
Valtonen: No acute emergency
Meanwhile, Finnish Foreign Minister Elina Valtonen (NCP) appeared less alarmed about the Greenland situation than some of her international counterparts.
"There is no acute emergency," she said on Yle's discussion programme A-studio on Wednesday night.
Earlier the same day, it was reported that Sweden had sent troops to Greenland, which is an autonomous territory of Denmark, while Norway sent two military officers there. Germany is also gearing up to send naval and air force troops, too.
Finland has also been asked to take part in military exercises in Greenland, and according to Valtonen, that request is being considered.
She said the exercises would be small in scale with the possibility of Nato joining in a larger operation in the region.
Valtonen said that in her opinion, any military preparations must be taken with the military alliance.
