Defence secretary Gavin Williamson expresses deep regret at resignation of 'close friend' James Mattis

US general had 'served their country for many decades both in uniform and outside of uniform'

Gavin Williamson said he had built up a 'close friendship and relationship,' with Jim Mattis. (Reuters)

Defence secretary Gavin Williamson has spoken of his deep regret as well as huge respect at the departure of his American counterpart, James Mattis, who left Donald Trump's administration in protest at the US president’s foreign policy.

In his resignation letter the former Marines General implicitly criticised Mr Trump, who had repeatedly attacked Nato while failing to condemn Vladimir Putin, saying “my views on treating allies with respect and also being clear-eyed about both malign actors and strategic competitors are strongly held and informed by over four decades of immersion in these issues”.

Gen Mattis, according to defence and diplomatic sources was strongly opposed to Mr Trump’s decision to withdraw forces from Syria and cut troop numbers in Afghanistan by half.

Speaking during a visit to Ukraine, Mr Williamson said he treated Gen Mattis’s departure with obvious “sadness when you’ve built up a close friendship and relationship with someone and someone who has served their country for many decades both in uniform and outside of uniform.

“You’ve got to see what Jim has achieved in his time as defence Secretary," he said. "He’s really been quite transformational in what the US armed forces have been able to do, extra investment going in and you’ve seen a massive increase in investment here in Europe...Jim has been an important part of that transformation.”

Discussing whether the US cutback will affect British forces who are also engaged in Syria and Afghanistan, Mr Williamson added: “We’ll continue to work as a Nato alliance. [Operation] Resolute Support is an alliance of many different nations and it’s not just the United States and it’s not just the United Kingdom, it’s other countries whether it’s Georgia, whether it’s Mongolia, whether it’s Australia - so many nations all coming together, working together with the Afghan government to rebuild Afghanistan...”

Mr Williamson wanted to stress that “Daesh (Isis) remains a real threat to us in the UK and we need to confront them wherever they are. We need to keep them under pressure we need to remain on the front foot. “

Asked whether the UK will seek to fill some of the gap left by the Trump withdrawal with European allies, Mr Williamson said: “We shall continue to liaise with our allies to see what steps need to be taken to protect ourselves.”

The Defence Secretary still held out hope that the US would continue to play a part in Afghanistan.

He said: “The US, as the world’s global superpower, I have no doubt will continue to be very heavily involved in Afghanistan..... It is quite clear in terms of their commitment to the peace process, driving the peace process forward, this is an important part of what they are going to continue to be doing in terms of Afghanistan. The US has had a major investment in Afghanistan, obviously that will continue to change and fluctuate over the years ahead.”