Pakistani police have arrested a mentally disabled 11-year-old girl after a mob accused her of desecrating pages of the Koran.

The mob demanded the Christian girl's arrest and threatened to burn down Christian homes outside the capital Islamabad, local media say.

Officials said the girl could not properly answer police questions.

Her parents have been taken into protective custody following threats and other Christian families have fled.

It is thought that the girl has Down's syndrome.

Paul Bhatti, Pakistan's minister for National Harmony, told the BBC that the girl was known to have a mental disorder and that it seemed "unlikely she purposefully desecrated the Koran".

"From the reports I have seen, she was found carrying a waste bag which also had pages of the Koran," he said.

"This infuriated some local people and a large crowd gathered to demand action against her. The police were initially reluctant to arrest her, but they came under a lot of pressure from a very large crowd, who were threatening to burn down Christian homes."

He said more than 600 people have fled from the Christian neighbourhood.

Rights activists have urged Pakistan to reform its controversial blasphemy laws, under which a person can be jailed for life for desecrating the Koran.

Many of those accused of blasphemy have been killed by violent mobs, while politicians who advocate a change in legislation have also been targeted.

Last year, Shahbaz Bhatti, the minister for minority affairs, was killed after calling for the repeal of the blasphemy law.

His death came just two months after the murder of Punjab Governor Salman Taseer, who also spoke out about the issue.