A British teacher has been charged in Sudan with insulting religion, inciting hatred and showing contempt for religious beliefs.
Colleagues of Gillian Gibbons said she made an "innocent mistake"
The Foreign Office has confirmed that charges have been laid against Gillian Gibbons, 54, from Liverpool.
She was arrested in Khartoum after allowing her class of primary school pupils to name a teddy bear Muhammad.
Foreign Secretary David Miliband has said he will summon the Sudanese ambassador "as a matter of urgency".
In a statement, Prime Minister Gordon Brown said he was "surprised and disappointed" at the charges.
A spokesman said the first step was to "understand the rationale behind the charge", something which would be discussed by Mr Miliband and the ambassador as soon as possible.
"We will consider our response in the light of that," he added.
Lawyers say Mrs Gibbons faces six months in jail, 40 lashes or a fine if convicted.
Sudanese state media said prosecutors had completed their investigation and decided to charge Mrs Gibbons under Article 125 of the Sudanese criminal code.
The BBC's Amber Henshaw, in Khartoum, said Mrs Gibbons was expected to appear in court on Thursday.
The Muslim Council of Britain reacted angrily to the news, saying it was "appalled" and demanded Mrs Gibbons' immediate release.
"This is a disgraceful decision and defies common sense. There was clearly no intention on the part of the teacher to deliberately insult the Islamic faith," said Secretary-General Dr Muhammad Abdul Bari, in a strongly-worded statement.
"We call upon the Sudanese President, Omar al-Bashir, to intervene in this case without delay to ensure that Ms Gibbons is freed from this quite shameful ordeal," said Dr Bari.
Mrs Gibbons taught at the fee-paying Unity High School in Khartoum and the school's director, Robert Boulos, said earlier: "This is a very sensitive issue. We are very worried about her safety.
Earlier, the Sudanese Embassy in London said the situation was a "storm in a teacup" and signalled that the teacher could be released soon, attributing the incident to a cultural misunderstanding.
But Sudan's top clerics have called for the full measure of the law to be used against Mrs Gibbons and labelled her actions part of a Western plot against Islam.
"What has happened was not haphazard or carried out of ignorance, but rather a calculated action and another ring in the circles of plotting against Islam," the Sudanese Assembly of the Ulemas said in a statement.
The semi-official clerics body is considered relatively moderate and is believed to have the ear of the Sudanese government.
A Sudanese human rights lawyer and Member of Parliament countered that Mrs Gibbons may be acquitted or simply fined under the discretion of the magistrate.
"It is not imperative to lash her, it is not imperative to send her to prison," said Ghazi Suleiman. "But I think the lady, she hasn't got any intention to insult the Islamic religion, therefore I am sure, very sure that if she went to the court she might be acquitted."
Mrs Gibbons was arrested on Sunday after several parents made complaints to Sudan's Ministry of Education.
The BBC's security correspondent Frank Gardner said the situation could potentially become a very serious diplomatic incident.
Catherine Wolthuizen, chief executive of Fair Trials International, told BBC News 24 that getting fair legal representation for Mrs Gibbons is a priority: "We are shocked and dismayed as I think many people are."