Ukrainian President Volodymyr Zelenskiy said on Monday that thousands of Russian troops were gathering for a new offensive in the east, and that Russia would not suspend its military operation in Ukraine for further peace talks. read more Despite resupply efforts in Donbas, the United States did not believe this was the beginning of a new offensive in the region, the official said, speaking on condition of anonymity. Sign up now for FREE unlimited access to Reuters.com Register “We believe this is an attempt to strengthen and supply their forces in Donbas, they are still north of Izium,” the official told reporters, referring to a town about 180 km (112 miles) north of Donetsk. The Russian vehicles sent to the area included command and control elements and support personnel for aircraft and infantry units, the official said. Last week, Russia completed its withdrawal from around Kyiv and sent some troops to Belarus to refresh and refuel. The official said there was evidence that some of these troops in Belarus were moving east. Russia still had the vast majority of its regular battalion groups in Ukraine, including more than 55 groups in the south. The Russian Defense Ministry said that Russian missiles fired from the sea destroyed on Sunday the S-300 anti-aircraft missile systems that had supplied Ukraine with a European country. The official said the United States had seen an airstrike at Dnipro airport that destroyed some infrastructure, but had no evidence that any S-300 missile defense system had been destroyed by Russia. Over the weekend, US Secretary of Defense Lloyd Austin spoke with a small number of Ukrainian soldiers who were in the United States for military training when the Russian invasion began. The troops were trained on Switchblade drones while in the United States and were scheduled to return to Ukraine on Sunday. The official was unaware of any current plans to bring Ukrainian forces to the United States for training, but Washington was considering various options on how Ukrainians could be trained to use such drones. Sign up now for FREE unlimited access to Reuters.com Register Report by Idrees Ali and Christopher Gallagher. curated by John Stonestreet and Grant McCool Our role models: The Thomson Reuters Trust Principles.