Leto made headlines weeks ago for paying tribute to Ukrainians while accepting the Best Supporting Actor prize for 'Dallas Buyers Club' at the 2014 Academy Awards, reported Digital Spy.
30 Seconds to Mars played a gig in Kiev's Maiden Square with Leto praising the Ukrainian people by waving the country's flag.
"You guys are in the midst of something really beautiful and it may be difficult, but there's no price too high to pay for the privilege of owning yourself," he said.
"And I want to let you know, I understand other bands have cancelled their shows, but there was no way, 30 Seconds to Mars wasn't going to be here in this beautiful city, in this great country here tonight.