Finland has agreed to join the France-led European Intervention Initiative which, once established, would be able to react to situations near European borders without assistance from NATO or the United States.
Speaking after a press conference with visiting French President Emmanuel Macron on Thursday, President Niinistö said that Finland will sign a letter of intent during the autumn.
So far, nine other EU countries have announced their decision to join Macron's coalition of the willing, including France, Germany, Belgium, Denmark, the Netherlands, Estonia, Spain, Portugal and the United Kingdom.
Paris is seeking a deployable European military crisis force outside of existing EU efforts.
Niinistö said that it is strategically important for everyone to know that Europe will stay united. The president added that Finland sincerely wants to be involved in building a safe Europe whose voice can be heard.
Meanwhile Macron, who arrived in Helsinki for an official visit on Wednesday, said he was pleased that Finland had decided to join the intervention force that would create a common defence strategy culture.
Macron added that he wanted to strengthen the EU foundation treaty to include an automatic solidarity clause that would be binding on all member states.
According to an official handout, the leaders planned to discuss security and defence policy, relations with Russia and the US, Arctic questions, climate change and “the state of the rules-based multilateral international order,” among other issues.