The head of Pakistan’s leading body of Muslim clerics Tuesday came to the defence of a young Christian girl accused of blasphemy, demanding her case be handled fairly and impartially.

Allama Tahir Ashrafi, chairman of the All Pakistan Ulema Council, said if Rimsha, accused of burning papers containing verses from the Quran, were found to be innocent, her accusers should face justice.

The cleric said protesters who demonstrated to demand punishment for Rimsha, who reportedly suffers from Down's Syndrome, were following the "law of the jungle".

Rimsha has been held since August 16 under the strict blasphemy laws, prompting concern from Western governments and the Vatican and anger from rights groups.

On Monday Rimsha was taken from prison to hospital for tests to determine how old she was, a senior doctor told AFP, after conflicting reports about her age.

Around 120 uniformed police officers guarded the hospital, the doctor said.

Ashrafi urged the government to take action to protect Christians in the poor Islamabad suburb of Mehrabad, where Rimsha lives, and encourage Christian families who fled in fear after the incident to return.

"This is inhuman that those who have nothing to do with the case or are not a party to it are also being harassed," Ashrafi told AFP.

"It is just like the law of jungle that 500 people approached a police station and got a report forcibly lodged with the police."

Blasphemy is an extremely sensitive subject in the nation of 180 million people, 97 percent of whom are Muslims, and those convicted of defaming Islam or desecrating the Koran can face life imprisonment or even the death penalty.

Human rights activists have warned the laws are often used to settle personal vendettas and last year two prominent politicians were assassinated for speaking out against the legislation.

Ashrafi said Rimsha's case should be a watershed for Pakistan's blasphemy laws.

"We demand an impartial and thorough investigation into the case. Strict action should be taken against all those accusing the girl if she is found innocent," he said.

"The government should make this case an example so that nobody will dare misuse the blasphemy law in future."

A medical examination on Monday determined Rimsha's age as "around 14", the doctor at Federal Government Services Hospital told AFP on condition of anonymity.

Rimsha's lawyer Tahir Naveed Chaudhry said they had applied to have her case proceed under juvenile law.

At a brief hearing in the case on Tuesday, Judge Raja Jawad Hassan adjourned proceedings until Thursday after defence lawyers submitted a bail application.