Image copyright Getty Images Image caption The EU is to hit back with tariffs on Harley Davidson motorcycles

The prime minister has told President Trump that new US steel and aluminium tariffs are "unjustified and deeply disappointing".

Theresa May was speaking in a 30-minute phone call with Mr Trump that UK officials described as "constructive".

Downing Street said Mrs May underlined the need to safeguard jobs and they agreed to discuss it further at the G7.

International Trade Secretary Liam Fox said the response to the US tariffs must be "measured and proportionate".

He told MPs: "It is right to seek to defend our domestic industries from both the direct and indirect impacts of these US tariffs ... it's important that the United Kingdom and the EU work within the boundaries of the rules-based international trading system."

The US tariffs of 10% on aluminium and 25% on steel from the EU, Canada and Mexico have been widely condemned.

French President Emmanuel Macron has called Mr Trump to tell him the tariffs were "illegal", while Canadian Prime Minister Justin Trudeau has said the US move is "totally unacceptable".

The EU, Mexico and Canada have all set out plans for retaliatory tariffs on US goods.

At the weekend, China - which is not directly impacted by last week's announcement - warned that all trade talks between Beijing and Washington would be void if the US sets up trade sanctions.

Despite the chorus of criticism, Mr Trump appeared in no mood for compromise. On Saturday, the president tweeted that the US had been "ripped off by other countries for years on trade".

He says steel tariffs will protect US steelmakers, which he says are vital to national security.

Mr Trump has also complained about barriers US firms face in Europe and elsewhere. "Time to get smart!" he added.

Trade sanctions: The basics

What is a trade war? It's when countries attack each other's trade with taxes and quotas. One will raise tariffs, a type of tax, causing the other to respond, in a tit-for-tat escalation. This can hurt economies and lead to rising political tensions.

It's when countries attack each other's trade with taxes and quotas. One will raise tariffs, a type of tax, causing the other to respond, in a tit-for-tat escalation. This can hurt economies and lead to rising political tensions. What are tariffs? Taxes on products made abroad. In theory, taxing items coming into the country (imports) makes people less likely to buy them as they become more expensive. They're likely to buy cheaper local products instead, boosting your country's economy.

Taxes on products made abroad. In theory, taxing items coming into the country (imports) makes people less likely to buy them as they become more expensive. They're likely to buy cheaper local products instead, boosting your country's economy. What's a trade deficit? The difference between how much your country buys from another country, compared with how much you sell to that country. The US has a massive trade deficit with China. Last year, it stood at about $375bn.

Canada, Mexico and the EU combined exported $23bn worth of steel and aluminium to the US in 2017 - nearly half of the $48bn of total steel and aluminium imports last year.

The EU has responded to the US announcement with a 10-page list of tariffs on US goods ranging from Harley-Davidson motorcycles to bourbon.

Canada plans to impose tariffs of up to 25% on about $13bn worth of US exports from 1 July. Goods affected will include some American steel, as well as consumer products such as yoghurt, whiskey and coffee.