Pope Francis minced no words aboard the papal plane on Monday when he told the world's more than 1 billion Catholics that they need not breed "like rabbits." the Associated Press reported.

The pope was traveling from Manila to Rome at the end of his week-long Asia trip and invited journalists to an hour-long news conference. Members of his faith should practice "responsible parenting," which requires that couples regulate the births of their children in accordance with church teaching, the pontiff argued, according to The Associated Press. 

Catholic doctrine prohibits artificial contraception, but the pope said there were many "licit" ways of regulating births that are approved by the church. The AP interpreted the remark as a reference to the Natural Family Planning method of monitoring a woman's cycle to avoid sex when she is ovulating.

During an hour-long news conference on the plane from Manila to Rome, Francis used "unusually frank language," according to the New York Post as he spoke at length about birth control and population.

"Some think, excuse me if I use the word, that in order to be good Catholics, we have to be like rabbits -- but no," Pope Francis said.

According to the AP, the pope's family-planning comments received particular attention because they "signal that he is increasingly showing his more conservative bent."

Rabbit breeders in Germany, meanwhile, told the Telegraph that they were not amused by pontiff's comments. 

"Contrary to popular opinion, rabbits do not have a rampant sex drive, and that the pope should have chosen his words more carefully," the newspaper explained.

Erwin Leowsky, the president of the German Rabbit Breeders Association, said Pope Francis' allusion was "stupid." 

In addition, the pope called the pregnancy of a woman who had already had seven children by Caesarean sections an "irresponsibility."

Pope Francis also touched on other topics, including corruption and his future travel plans.

He said he once chastised two Argentine bureaucrats after they tried to involve him in a kickback scheme and announced his intention to visit the Central African Republic and Uganda late this year, as well as Ecuador, Bolivia and Paraguay in 2016.