US Secretary of State Antony Blinken urged western nations Wednesday to remain united in the face of what he called "relentless" Russian aggression against Ukraine and reassured Ukraine's leader of their support.

Blinken told Ukrainian President Volodymyr Zelenskyy during a visit to Kyiv that the U.S. And its allies were steadfast in backing his country and its democratic aspirations amid growing fears of a potentially imminent Russian invasion.

"The Ukrainian people chose a democratic and European path in 1991. They took to the Maidan to defend that choice in 2013, and unfortunately ever since you have faced relentless aggression from Moscow," Blinken said, referring to Ukraine's trajectory since the collapse of the Soviet Union.

"Our strength depends on preserving our unity and that includes unity within Ukraine," he said to Zelenskyy. "I think one of Moscow's long-standing goals has been to try to sow divisions between and within our countries and quite simply, we cannot and will not let them do that." The Biden administration said earlier it was providing an additional $200 million in defensive military aid to Ukraine to help protect its sovereignty and territorial integrity. Zelenskyy thanked Blinken for the assistance, which was approved in late December but not formally confirmed until Wednesday, as well as for his visit and assurances of support.

 "This (military) support not only speaks to our strategic plans of Ukraine joining the alliance, but more importantly to the level of our military, our military supplies," he said, referring to Kyiv's desire to join NATO over Russia's strong objections. "If we want dramatically fast steps in modernizing the military, we need help especially in these tough times," Zelenskyy said. "Your  visit is very important.

It underlines once again your powerful support of our independence and sovereignty." The aid announcement came at the start of Blinken's hastily arranged visit as U.S. And western officials stepped up increasingly dire warnings about a possible Russian invasion.

Blinken said Russian President Vladimir Putin is now in position to launch military action against Ukraine at will and at very short notice with more than 100,000 troops massed on its border and plans to add more. "We know that there are plans in place to increase that force even more on very short notice and that gives President Putin the capacity, also on very short notice, to take further aggressive action against Ukraine," Blinken told staff at U.S. Embassy in Kyiv.