Theresa May will use the upcoming G7 meeting in Canada to press Donald Trump to reverse tariffs introduced on European steel and aluminium, Liam Fox has said.

The decision by the US president to add 25% and 10% tariffs respectively to the metal imports was wrong and illegal, the international trade secretary said. But while he said EU counter-actions had so far been proportionate, he cautioned against measures that might spark a full-blown trade war.

The international trade secretary told BBC Radio 4’s Today that the UK was still seeking tariff exemptions based both on specific products and also geographic location. He said: “We will still be making that case throughout this week. We of course have the G7 leaders meeting at the end of the week, where the prime minister will be raising this with President Trump alongside other leaders.

“The United States believes – I believe wrongly and illegally – that this is a national security matter for the US. Given that we export some pretty complex steel products to the United States, which are part of their national security programmes themselves, this reasoning that is given is wrong and therefore we believe unlawful.”

On Friday May said she was disappointed by “the unjustified decision by the US to apply tariffs to EU steel and aluminium imports”.

She said: “The US, EU and UK are close allies and have always promoted values of open and fair trade across the world. Our steel and aluminium industries are hugely important to the UK, but they also contribute to US industry, including in defence projects which bolster US national security.”