Pregnancy is the biggest killer of teenage girls worldwide, a charity has said.

Every year one million teenage girls die or are injured because of pregnancy or childbirth, according to Save the Children.

In a new report, the children's charity warns that girls under 15 are five times more likely to die in pregnancy than women in their 20s.

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More than 25,000 girls under 18 are married every day, according to the report. Many quickly fall pregnant before their bodies have sufficiently developed.

"The issue of children having children - and dying because their bodies are too immature to deliver the baby - is a global scandal," said Save the Children's chief executive Justin Forsyth.

"This is a tragedy not just for those girls but also for their children - babies are 60% more likely to die if their mother is under 18.

"In the developing world, family planning isn't just a lifestyle choice. Children's lives depend on it."

The report also found that around the world, one in five girls are teenage mothers - having given birth to a child by the time they are 18.

Next month a family planning summit is to be held in London to discuss increasing the global availability of contraceptives and to empower women so they have more choices about sex.