With millions of YouTube views and hits on Spotify and iTunes, a group of young nun rockers play one of their biggest gigs next week, and thousands of Catholics, including the pope himself, will lap it up.

It may be rock and roll, but Twisted Sister they ain't, and sex and drugs are not an option for the Sisters of the Servants of the Plan of God. They play their brand of melodic rock in their traditional habits.

"We're young sisters," says 37-year-old guitarist Sister Ivonne of the band, which includes members from Chile, Japan, Ecuador, China and Costa Rica.

"This is another form of bringing our evangelical message, showing our strength -- that's to say, it's also music that we like, it shows a lot about who we are."

Sister Ivonne (L) says playing in a band with other nuns is "another form of bringing our evangelical message, showing our strength" / © AFP

Known as "Siervas" or Servants, the band plays catchy Christian songs that sound indistinguishable from many of their peers in mainstream rock.

But the appearance is very different, rock's grunge and glad rags giving way to the nuns' tried and trusted black and white habits and veils on stage.

- YouTube hit -

Sister Teresa, a drum player from Chile, plays in a band made up of nuns she says takes "the word of God and his consolation to the prisons, to the disabled" / © AFP

With a half-dozen slickly produced videos on YouTube, Siervas has built an international following as it communicates its message of "love, joy, hope."

Their "Trust in God" music video, which features the nuns playing on a helipad atop a Lima skyscraper, went viral on YouTube with nearly two million views.

And now, the Peru-based sisters will play at the World Youth Day celebrations, a gathering of global Catholic youth in Panama presided over by Pope Francis.

The message at the heart of their music? "We want to reach as many people as possible, and if the pope is included in that, we're more than satisfied," said Ivonne, who pens much of the lyrics.

The 11-member band, which performs in Spanish, has previously played for crowds at Francis' visits to Mexico and Peru.

- Not just music -

Sister Arisa, a violinist from Japan, says that "it was God's plan" that she and other nuns form a band / © AFP

"We're not just working in music, but we take the word of God and his consolation to the prisons, to the disabled," said Sister Daniela, the drummer from Costa Rica.

Tuesdays, when they are back in Peru, they bring food to the homeless on the streets.

The group will gig at a women's prison during the trip to Panama. They will also play at a children's cancer hospital and schools.

"We go to the women's prisons to listen to them. All they ask is to be listened to and to know God has forgiven them," said Camila, the 22-year-old Peruvian guitarist.

The band, which has so far visited 11 countries, including the United States, was formed in Lima in 2014 when the young musician nuns from different nationalities came together, said 24-year-old Sister Arisa, from Japan.

"It was God's plan that we come together," said Arisa, a violinist.

After months of rehearsal, they held their first concert in the auditorium of the General Command of the Army, helping raise funds for a house for the order in Angola.

The band has undergone several changes to its lineup since 2014, as sisters leave to fulfill their missionary role.

"Until now we have not been able to talk to the pope, we would love it if he approaches us," said Ivonne, from Chile.

"I wouldn't know what to say, I think I would faint."