<b>Live updates: follow the latest news on </b><a href="https://www.thenationalnews.com/world/2022/02/18/russia-ukraine-latest-news/"><b>Russia-Ukraine</b></a> Ukrainian resistance fighters have endured another week of fighting and remain “determined”, a senior defence official said on Friday at a Pentagon press briefing — and that Russian intelligence miscalculated the will of the ragtag Ukrainian fighters. “[They are] being very strategic about how they're defending and where they are putting their resources where they're most needed,” the official said, noting they are using hit-and-run tactics to great advantage. “They are doing it quickly. They are being adaptive and nimble,” The official also noted that the Russians haven't properly carried out their logistics plan and have demonstrated little in the way of sustainability, though it is expected that they are “going to work through those challenges and we're beginning to see them do that”. The official discouraged <a href="https://www.thenationalnews.com/world/us-news/2022/03/09/how-are-us-and-canadian-army-veterans-getting-to-ukraine/" target="_blank">US veterans from travelling to Ukraine to assist in the fighting</a> and instead suggested making a contribution to organisations such as the Red Cross. Since the war began two weeks ago, the Pentagon estimates the Russians have launched more than 800 missiles into Ukraine. The last time Russian forces carried out such a large-scale ground operation using combined air, land and sea forces was during the Second World War. Combined arms integration is difficult to achieve in any scenario by any country, the official said. Russian forces are now only <a href="https://www.thenationalnews.com/world/us-news/2022/03/11/russian-forces-are-15km-from-ukraines-capital-pentagon-says/" target="_blank">15 kilometres from Kyiv's city centre</a>, putting them even closer to civilian populations. They are also on the outskirts of Kharkiv, where Ukrainians are putting up a fierce resistance. <a href="https://www.thenationalnews.com/world/europe/2022/03/11/russias-destruction-of-ukraines-mariupol-from-above-in-pictures/" target="_blank">The city of Mariupol</a> is under increasing pressure, but is also being well defended, the Pentagon official said. The Russian convoy in the north of Ukraine has not made any significant progress, with some of their vehicles having moved off the road and into the tree line, presumably for force protection against Ukrainian attacks. The Ukrainians have about 56 fighter jets available and are flying about five to 10 sorties per day. The Pentagon official noted that they do not really need to do more than that as the Russians have surface-to-air missiles that could knock those planes out of the sky. In addition, the Ukrainians have made great use of their <a href="https://www.thenationalnews.com/world/2022/03/11/russian-tank-losses-mount-in-face-of-ukraine-drone-grenade-tactics/" target="_blank">drones</a>, which can deliver munitions as well as intelligence, surveillance and reconnaissance, the official said. The US and 14 allies continue to send defensive weapons systems into Ukraine, including small arms, anti-armour and air defences.