Vatican City, May 8 - Pope Francis told a group of nuns at Wednesday's general audience in St Peter's Square to embrace their maternal side and to "be mothers". "Chastity should be fertile, it generates spiritual children," the pope told some 800 nuns from numerous religious orders. "Motherhood is sacred...you must be mothers and not old maids," Francis said. "Excuse me if I speak this way...be mothers, as figures of the mother church, you cannot understand Mary and the Church without motherhood, and you are icons of Mary and the Church". While emphasising the role of women in the Church, Pope Francis has also maintained a critical position on the majority of American nuns for deviating from official Catholic doctrine by promoting "radical feminist themes" and devoting too much time to social justice while remaining quiet on issues such as birth control and same-sex marriage.