He stated this during a military parade in Kyiv on Thursday on the occasion of the 26th anniversary of Ukraine's independence, an Ukrinform correspondent reports.
"In total, 10,000 Ukrainian lives are on the conscience of the aggressor. We will never forget it, and we will never forgive it," Poroshenko said.
He also mentioned Ukrainian servicemen who were killed in the battle of Ilovaisk in Donetsk region in 2014.
According to official figures, 366 Ukrainian soldiers were killed (157 not identified) near Ilovaisk, and 158 more are missing.