Three Green MEPs – including one from the UK – have been arrested after breaking into a Belgian military airbase to protest against its stockpiling of American B61 nuclear bombs.

The MEPs – Molly Scott Cato, Michèle Rivasi and Tilly Metz – unfurled a banner on a runway for F-16 fighter jets at the Kleine Brogel base in the east of the country calling for a nuclear-free Europe, before being taken into custody.

Another Green MEP, Thomas Waitz, was arrested in a demonstration outside the base, along with 11 other activists from the Belgian peace group Agir pour la Paix (Act for Peace), three of whom also scaled a 3.5-metre fence to get into the base.

The direct action protest follows the US withdrawal from the intermediate-range nuclear forces (INF) treaty earlier this month.

About 150 US nuclear weapons are thought to be scattered across Europe in Belgium, Germany, Italy and the Netherlands, compared with more than 7,000 at the peak of the cold war.

But campaigners fear this number could rapidly rise in any new arms race, and say each B61 has an explosive yield of up to 340 kilotons, 23 times more powerful than the bomb that devastated Hiroshima.

On Tuesday, Scott Cato, the MEP for South West England, told the Guardian that the protest would be “a balance of risks and purposes”.

She said: “When you’re talking about the potential end of the world, your own personal safety is put into perspective – and we are talking about weapons that could kill millions of people.”

“Nuclear weapons offer no solution in this era and no rationale for defending the people in the south-west who I represent, one of whom died this year because of a Russian secret forces attack. How are nuclear weapons supposed to help Dawn Sturgess?” she said, referring to the woman police believe was killed by novichok in Amesbury, Wiltshire last year.

MEPs in Brussels enjoy some immunity from prosecution but it is unclear if this would cover state security laws, which carry potential five-year prison sentences.

Michèle Rivasi, the vice-chair of the Green party in the European parliamentsaid on Tuesday that: ““We are demanding the withdrawal of nuclear bombs at Kleine Brogel and also from Italy, Germany and the Netherlands. We urge all EU member states to sign and ratify the treaty prohibiting nuclear weapons. Our first objective is a Europe without nuclear arms.”.”

Only 21 nations have ratified a 2017 UN treaty prohibiting nuclear weapons. Of the EU countries, only Austria has signed up, although Ireland may soon follow.

The nuclear shadow over Europe has loomed large across Europe in the last year, after Russia’s deployment of Iskander missiles in Kaliningrad, Germany’s exploration of nuclearisation and France’s flexing of its nuclear muscle, as Brexit approaches.

Green party sources say Wednesday’s action was, in part, an effort to set the political agenda before elections in Belgium – where the Greens top opinion polls – and across northern Europe, where they are riding high.