Britain's Prime Minister Boris Johnson has promised to provide additional military aid to Ukraine, after President <a href="https://www.thenationalnews.com/world/uk-news/2022/04/23/zelenskyy-thanks-uk-for-training-ukraine-military/" target="_blank">Volodymyr Zelenskyy</a> told him what was needed to defend the country against Russian forces. In a call on Saturday afternoon, the prime minister offered Mr Zelenskyy the UK’s “continued economic and humanitarian support”, a representative of his Downing Street office said. Mr Johnson is said to have told Mr Zelenskyy that he is “more committed than ever to reinforcing Ukraine and ensuring Putin fails”. Britain is one of the largest suppliers in Europe of arms to <a href="https://www.thenationalnews.com/world/europe/2022/04/25/russia-wont-win-this-war-says-ukraines-zelenskyy/" target="_blank">Ukraine</a>, having already sent more than 5,000 anti-tank missiles, 1,360 anti-structure munitions, five air defence systems with more than 100 missiles, and 4.5 tonnes of plastic explosives, figures compiled by the Ministry of Defence show. Ukrainian forces have also been using Starstreak high-velocity and low-velocity anti-air missiles supplied by the UK. Following the call between Mr Johnson and Mr Zelenskyy, a Downing Street office representative said: “The prime minister spoke to Ukrainian President Volodymyr Zelenskyy today, as part of their regular dialogue. President Zelenskyy tweeted: “I keep in touch with @BorisJohnson. Spoke about the situation on the battlefield and in the blocked Mariupol. “Discussed defensive support for Ukraine and the necessary diplomatic efforts to achieve peace.” Later, Mr Johnson tweeted: “I spoke to President @ZelenskyyUa earlier to set out how the UK will continue to provide military and humanitarian aid to give Ukrainians the equipment they need to defend themselves. “I’m more committed than ever to reinforcing Ukraine and ensuring Putin fails.” Meanwhile, the Foreign Office is investigating reports that a British citizen has been detained by Russia after a video emerged showing a man dressed in camouflage being questioned. In the video, reportedly shown on Russian television, the man appears to give his name as Andrew Hill. He speaks with an English accent, has his arm in a sling, a bandage around his head, and blood can be seen on his hand. The video, which has not been verified, has been shared online. The Foreign, Commonwealth and Development Office is investigating the reports and also supporting family members. The Foreign Office said it condemned the exploitation of prisoners of war for political purposes and that anyone detained had the right to be treated humanely in accordance with the requirements of international humanitarian law. Two other British men, said to be working as humanitarian aid volunteers, are also believed to have been detained in Ukraine by Russian forces. The Presidium Network, a non-profit group, said Paul Urey and Dylan Healey were captured early on Monday morning at a checkpoint south of the city of Zaporizhzhia in south-eastern Ukraine. Mr Urey, who was born in 1977 and is from Manchester, and Mr Healey, born in 2000 and from Cambridgeshire, travelled to Ukraine of their own accord, the organisation said. They were not working for the Presidium Network, which helps to send aid into Kyiv. The organisation said the pair were driving to help a woman and two children to leave the country when they went missing. Presidium Network said it is concerned that Russian forces may believe the two men are British spies. The Foreign Office said it was urgently seeking more information following reports of British citizens being detained in Ukraine. In an intelligence update on Saturday morning, the Ministry of Defence in the UK said Russia faces “considerable challenges” and troops are possibly suffering from “weakened morale”.