"Either we are part of an alliance like NATO and also make our contribution to strengthen this Europe, or we have only one option; to rearm ourselves," the Ukrainian ambassador to Germany, Andriy Melnik, said.
Speaking to national public radio Deutschlandfunk on Thursday, Melnik raised the possibility that the former Soviet republic would seek to acquire nuclear weapons and the means to deliver them that it gave up after the Soviet Union broke up in 1991.
"How else could we guarantee our defence?" Melnik queried.
Ukraine was once in possession of the third-largest nuclear arsenal in the world, but disarmed in 1994 after receiving security guarantees from the United States, Russia and Britain.
It expressed anger following the 2014 annexation by Russia of the Crimean Peninsula, part of its territory, that the guarantees had not been lived up to.
Ukraine has for years sought to launch accession talks with NATO but has thus far been turned down. The issue has acquired renewed urgency since the massing over recent weeks of tens of thousands of Russian troops along its border.
Parts of Ukraine's eastern Donetsk and Luhansk regions along the Russian border have been controlled by rebels supported by Moscow for nearly seven years.