Sir Keir Starmer has said that Russia started the Ukraine war and “could end the conflict straight away”.

The prime minister has arrived in Washington DC for talks with President Joe Biden at the White House over the ongoing conflict.

Sir Keir has backed Kyiv’s right to defend itself after Russian leader Vladimir Putin suggested his country would be “at war” with NATO if the West allows long-range weapons to be used against it.

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The PM said the UK does not “seek any conflict with Russia”, before adding: “That’s not our intention in the slightest.”

The UK has been providing Ukraine with Storm Shadow cruise missiles since last year but, like the US, it does not allow the country to launch the weapons against sites in Russia amid fears of escalation.

Ukrainian President Volodymyr Zelenskyy has been calling for restrictions to be lifted on the use of such missiles against targets in Russia, which launched a full-scale invasion of his country in February 2022.

On Thursday, President Putin said allowing long-range strikes “would mean that NATO countries, the US, and European countries are at war with Russia… if this is so, then, bearing in mind the change in the very essence of this conflict, we will make appropriate decisions based on the threats that will be created for us”.

Responding to his remarks, Sir Keir told reporters on the flight to the US: “Russia started this conflict. Russia illegally invaded Ukraine. Russia could end this conflict straight away.

“Ukraine has the right to self-defence and we’ve obviously been absolutely fully supportive of Ukraine’s right to self-defence – we’re providing training capability.”

UK Foreign Secretary David Lammy and US secretary of state Antony Blinken held talks with President Zelenskyy in Kyiv earlier this week as Ukraine continued to appeal to the two countries to change their stance – especially in light of American intelligence that Russia had received a shipment of weapons from Iran.

But while neither politician would reveal any decision, both Mr Lammy and Mr Blinken confirmed they would pass on the message to their respective leaders before they met at the end of the week, with the latter telling Sky News that President Biden was “not ruling out” moving his position.

It will also be the first time Sir Keir and President Biden meet after the UK government chose to ban some weapons export licences to Israel amid the ongoing conflict in Gaza.

Mr Lammy announced the decision in the Commons last week after legal advice to the government said there was a “clear risk” they might be used to commit “a serious violation of international humanitarian law”.

But he faced a backlash, both from MPs who thought the move undermined the UK’s support for Israel and from MPs who wanted the ban to cover all weapons export licences.

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On the same day, President Biden said a final hostage deal between Israel and Hamas was “very close” – but that Prime Minister Benjamin Netanyahu was not doing enough to secure an agreement.