Fighting in Ukraine has slowed to a grinding slog, with limited advances by either side and heavy casualties suffered for small territorial gains. With Russian forces hardening their defenses, making it more difficult for Kyiv's troops to gain ground, Ukraine's international supporters aim to help change the equation with the provision of armored vehicles that would aid new offensive operations, AFP said. Kyiv has welcomed pledges of further equipment, but is still pushing the countries backing its fight against Russia's invasion to follow Britain in agreeing to provide heavy Western tanks. Moscow's troops are "digging in, they're digging trenches, they're putting these Dragon's Teeth, laying mines. They're really trying to fortify that FLOT, that forward line of troops," US Undersecretary of Defense for Policy Colin Kahl said this week. Kahl said advances are currently measured in city blocks, or hundreds of meters (yards), and that the aim is to enable Ukraine "to change that dynamic with these kind of static defenses by being able to fire and maneuver through the use of more mechanized forces." Defense Secretary Lloyd Austin indicated on Friday that Ukraine was planning a new offensive by spring, and the United States and other countries have said they will give Kyiv a large number of armored vehicles that could play an important role in new advances. - 'Mechanized punch' - Washington pledged to provide 90 Stryker armored personnel carriers and 59 Bradley infantry fighting vehicles as part of a $2.5 billion aid package announced Thursday, after promising 50 Bradleys last week. Germany has said it would donate about 40 Marder infantry fighting vehicles, while France promised AMX-10 RC light tanks, and Britain answered Kyiv's requests for heavy Western tanks with a pledge to provide 14 Challenger 2s. The vehicles recently promised to Kyiv give Ukrainian forces "potentially a significant armored, mechanized punch," said Gian Gentile, a former US Army officer who is a senior historian at the RAND Corporation. Ukraine could use them "to try to carry out an offensive... similar to the kinds of gains that they made in Kharkiv last fall," he said, referring to a region where Kyiv's forces made significant advances against Russian troops. There are decreasing levels of firepower as well as protection when moving from heavy tanks to infantry fighting vehicles to armored personnel carriers, and they therefore fill different roles on the battlefield, Gentile said. For example, tanks are the best choice to take the lead when they may have to absorb hits from other tanks, while armored personnel carriers are better suited to delivering infantry to take a town. - Ukrainian offensive - Mark Cancian, a retired US Marine Corps officer who is a senior adviser at the Center for Strategic and International Studies, said that while the armored vehicles bound for Kyiv would have some defensive value, offense is the primary aim. "I think it's particularly focused on a Ukrainian offensive that everybody expects... later in the winter," he said. While pledges of armored vehicles have poured in, the United States has said it is reluctant to provide its Abrams tanks due to difficulties with maintenance and training, while Germany has so far declined to donate Leopard tanks. Ukrainian President Volodymyr Zelensky on Friday welcomed recent donations, but said there is "no alternative" to the West providing Kyiv with heavy tanks. Cancian said it would require a large number of such tanks to make a substantial difference on the battlefield, but noted that smaller donations could still add up while also having symbolic value for Zelensky as a show of Western support. The armored vehicles that have been promised will be complemented by a recently begun US program for Ukrainian forces focusing on joint maneuver and combined arms operations, which will train some 500 of Kyiv's troops per month. General Mark Milley, the top US military officer, said Friday that Ukrainian forces have to be "married up with the equipment, and then they got to be trained" for an offensive to be successful. "If you look at the weather and terrain etc., you can see that you have a relatively short window of time to accomplish both those key tasks. So that's very, very challenging to do that," Milley said.