VATICAN CITY — Pope Francis underscored migration and the narcotics trade as among the gravest ills plaguing the Catholic Church in Mexico and called on the country's bishops to help their flocks through solidarity and prayer.

The pope made his remarks May 19 to Mexican bishops making their periodic "ad limina" visits to the Vatican.

"I have learned much from what you have told me," he told the bishops, led by Cardinal Jose Francisco Robles Ortega of Guadalajara, president of the Mexican bishops' conference. "You leave me with serious worries about your churches."

"Some of your children who cross the border, all the problems of migration, those who don't make it to the other side. Children who die, children killed by hired assassins. All these serious problems," Pope Francis said.

"And then drugs, which is something you suffer from very seriously today," he said. "When a peasant tells you: 'What do you want me to do? If I raise corn I can live for a month, if instead I raise 'opium' I can live all year."

In response to such problems, the pope called on the bishops to seek what he called the "double transcendence."

"The first transcendence is in prayer to the Lord," he said. "It is the bishops negotiating with God for their own people. Don't forget it.

"And the second transcendence, closeness to your own people," he said. "With this double intention, forge ahead."

Pope Francis said the bishops had cause for hope because of their flocks' traditional devotion to Mary.

"I see that your church is established on very strong foundations, and you have a very strong tie with the mother of the Lord," the pope said. "And this is very important. It is very important. Mary will not leave you alone before so many problems, such dolorous problems."