US Defence Secretary Lloyd Austin arrived in Warsaw on Thursday after President Joe Biden said there was now every indication Russia was planning to invade Ukraine, including signs Moscow was carrying out a false flag operation to justify it, after Ukrainian forces and pro-Moscow rebels traded fire.
Russia denies planning to invade its neighbor and said this week it was pulling back some of the more than 100 000 troops it has massed near the frontier.
Washington says Russia is not withdrawing, but in fact sending more forces.
Ukraine and pro-Russian rebels gave conflicting accounts of shelling across the front in the Donbass separatist region.
The details could not be established independently, but reports from both sides suggested an incident more serious than the routine ceasefire violations reported regularly in the area.
Austin said Washington was “still gathering details, but we have said for some time that the Russians might do something like this in order to justify a military conflict”.
