Western countries are at the gates of a new cold war with Russia, sparked by the Ukraine crisis and a continuing failure to grasp the depth and seriousness of Vladimir Putin’s grievances with the US and EU, the Finnish president, Sauli Niinistö, has warned.

Speaking to the Guardian at his official residence before Thursday’s conference in Helsinki attended by the UK prime minister, David Cameron, and Nordic and Baltic state leaders, Niinistö said Finland had a long tradition of trying to maintain friendly relations with Russia. But it would not be pushed around.

“The Finnish way of dealing with Russia, whatever the situation, is that we will be very decisive to show what we don’t like, where the red line is. And that is what we are prepared to do,” Niinistö said, referring to recent violations of Finnish airspace by Russian military aircraft.

“We put the Hornets [US-made Finnish air force F-18 fighter aircraft] up there and the Hornets were flying alongside the Russian planes … The Russians turned back. If they had not, what would we have done? I would not speculate.”

A Finnish Air Force photograph shows a Russian AN-72 transport plane, taken by a Finnish aircraft pilot. Finland’s Defense Ministry said it suspects a Russian military aircraft on Thursday violated Finnish airspace Photograph: AP

Cameron will join eight Nordic and Baltic leaders at the one-day Northern Future Forum hosted by Alexander Stubb, Finland’s prime minister. Sources said they will discuss a response to Moscow’s official recognition of “illegitimate” weekend elections at the weekend that were won by pro-Russia separatists in eastern Ukraine, at a private dinner at Stubb’s residence at Kesäranta.

Cameron will be told Britain is seen as an essential player in formulating Europe’s policy towards Russia and that the Ukraine crisis shows how the EU is much stronger when its members work together.

Finland, formerly a grand duchy of the Russian empire, declared independence in 1917 after the Russian revolution. It survived two separate conflicts with the Soviet Union during the second world war. During the cold war, Finland followed a policy of “active neutrality” to keep Moscow at bay. The two countries share an 830-mile (1,300km) land border.

Many Finns worry that the insecurity and uncertainties of the cold war years are returning as the standoff with Russia over its annexation of Crimea and destabilisation of eastern Ukraine continues.

“We are in the position in the west of asking what is Putin up to,” Niinistö said. “Putin keeps saying the west and Nato are hostile. [He says] they have deceived Russia with Nato enlargement and they are undermining and humiliating Russia. “So this is a situation that is not promising. I have said we are almost at the gates of a new kind of cold war that could suck in all of Europe.'

Niinisto discussed the Ukraine situation with Putin in person in August and said he remained in touch with the Russian leader. He said the US and EU were partly to blame for not paying enough attention to Putin’s assertions that the west was weak, hedonistic and hostile to Russia’s values, including religious values. The EU had failed to appreciate its plans for closer ties with Ukraine posed a “huge problem” for Putin.

Putin, under pressure from Russian conservatives and ultra-nationalists, may have been emboldened by last year’s last-minute US decision not to launch bombing and missile attacks in Syria. Russia believed its diplomatic intervention at that time had been a great success, Niinisto said.

For Russia, Syria was only the latest example of perceived western weakness, an influential government insider in Helsinki said.

“A bigger factor is the consistent softness shown by the EU and the US when it comes to Russian actions. They [the Russians] have got away with murder since the first Chechen war and especially since [the Russian military intervention in] Georgia [in 2008],” the insider saidi.

Despite the rise in international tensions with Russia, a clear majority of Finns continues to oppose joining Nato, in part out of concern about Moscow’s possible reaction. Russian officials have repeatedly warned Finland, which is 100% dependent on Russian gas supplies, against taking up Nato membership.

But sentiment may be shifting ahead of Finnish general elections due next April, when relations with Russia and Nato will be a central issue along with the economy.

Niinistö said Finland was supportive of Nato and a contributor to Nato operations in Afghanistan. It also maintained large land forces, unlike some other EU countries. He rejected accusations that Finland was taking a free ride behind Nato’s protective shield.

“We are not passengers,” he said.

“We have a long tradition of keeping out of conflict with Russia … though we did not succeed in the second world war. We can’t change geography. We have a 1,300km border. That is more than all other EU countries together. The Nato-Russia border would be doubled [if Finland joined]. We have to consider that too.

“My main worry is the larger picture of getting close to a cold war. That would be a very uncertain situation and that worries us. But if you are asking are we afraid, directly or indirectly, of Russia, I would say no.”