BEIJING, China (Reuters) -- A panda once believed to be male and sent to Japan to breed with a female without success gave birth to twin cubs this week, state media reported on Thursday.

"Jinzhu was believed to be male owing to her inconspicuous secondary sex characteristic and behavior," the agency quoted Wei Rongping, assistant director of the reserve's research center, as saying.

Jinzhu was sent to Japan in 2000 to mate with a female, the report said.

"When the pandas showed complete disinterest, experts decided to turn to artificial insemination, leading to the discovery that Jinzhu had no penis," it added.

Jinzhu subsequently mated with a male in March 2007 and gave birth 142 days later, Xinhua said.