The Siberian tiger, native to northern China, southern Russia and parts of North Korea is on the brink of extinction in the wild, decimated by poaching and loss of habitat. Scientists believe only a few hundred now live outside captivity.
The cubs, now weighing 3 kilos (6.6 lb) each, were born on May 21 to six-year-old Gina and her mate, six-year-old Geo.
"It is a miracle," Liliana Stancu, chief of a zoo in the city of Galati in eastern Romania, told Reuters. "Their mother was extraordinary, accepting them, carefully looking after and feeding them from the very beginning."
"Without her help it would have been almost impossible for the little tigers to survive ... we try not to touch the cubs so as to not scare the mother into loosing the milk."
The mother, a 250-kilo cat, kept the cubs out of public view in an indoor den until this month.