A mother of two has become the first Christian woman in Pakistan to be sentenced to death for blasphemy.

Asia Bibi, a field labourer in her thirties, was handed the sentence by a court of sessions in Punjab province on Sunday evening.

She was found guilty of committing blasphemy against her fellow farm workers in the village of Ittanwali during a heated discussion about religion in June last year.

Some of the women workers had reportedly been pressuring Bibi to renounce her Christian faith and accept Islam. During the discussion, Bibi responded by speaking of how Jesus had died on the cross for the sins of mankind and asking the Muslim women what Muhammad had done for them.

The Muslim women took offence and began to beat Bibi and she was locked in a room by some men. According to partners of Release International, a mob reportedly formed and "violently abused" her and her children.

The charity, which supports persecuted Christians, said that blasphemy charges had been brought against Bibi because of pressure from local Muslim leaders.

Release International expressed its shock at Sunday's ruling.

"Pakistan has crossed a line in passing the death sentence on a woman for blasphemy," it said.

In addition to the death sentence, Bibi has also been fined more than £700 – equivalent to two and a half years' wages for an unskilled worker.

Release's partners in Pakistan say the sentence is a crushing blow for Bibi, who had been hoping to be acquitted and return to her husband and children.

"Although Asia has great courage, her dreams of release have vanished now. Please pray for her encouragement, strength and protection."

They are planning to visit Bibi in prison as soon as possible.

Release has launched a petition against Pakistan's blasphemy laws. It fears that the passing of the death sentence against Bibi could set a harmful precedent in other blasphemy cases.

Another Christian woman, Martha Bibi – no relation to Asia Bibi – is on trial in Lahore for blasphemy. She was accused of committing blasphemy after a dispute with builders in Kasur who reportedly refused to return equipment belonging to her.

Release said Pakistan's blasphemy laws were "wide open to abuse" and that Christians and other minorities were often accused of committing blasphemy by Muslims as a "vengeful way of settling scores".

He warned: "In effect Asia has been sentenced to death for sharing her Christian faith. In previous cases, the death sentence has not been carried out. But this could well mean a life sentence for Asia in appalling conditions on death row."

Release's online petition can be found at: www.releaseinternational.org/current