Russia's warning, including a call for foreign diplomats to flee the Ukrainian capital, marks a fresh escalation in the more than four-year war, with Moscow vowing "systematic" attacks on Kyiv, including on "decision-making centres".Rubio's offer came after Russia battered Ukraine over the weekend -- including firing its Oreshnik hypersonic missile -- and following a phone call with Russian Foreign Minister Sergei Lavrov."Every time you see these big strikes from one side or the other, it's a reminder of why this is a terrible war that's now gone on longer than the Second World War, and it needs to come to an end," Rubio told reporters during an official visit to India."The US stands ready and prepared to help do whatever we can to help facilitate the end of this war, and hopefully the opportunity will present itself at some point," Rubio said.An overnight Russian strike killed a 45-year-old man in Odesa, regional official Sergii Krasylenko said on Telegram early Tuesday.Russia's weekend barrage -- involving dozens of drones and missiles -- killed four people and caused widespread damage across the Ukrainian capital.Among the weapons Russia used was its Oreshnik hypersonic missile, which can travel 10 times the speed of sound and is capable of carrying nuclear warheads, according to Moscow.