Christian Solidarity Worldwide has expressed concern over recent reports that several key players involved in the case against four militants accused of assassinating Pakistani minorities minister Shahbaz Bhatti have received death threats from militant Islamist groups.

His brother, Paul Bhatti, has received a letter from the Tehreek-e-Taliban Pakistan (TTP) and Lashkar-e-Jhangvi (LeJ), warning him that he would suffer the same fate if he did not stop pursuing justice, Christian Solidarity Worldwide reports.

Shahbaz Bhatti was assassinated in his car in broad daylight in 2011 while on his way to his mother's home. It is believed he was murdered for his opposition to the country's blasphemy laws and his support of a Christian blasphemy defendant, Asia Bibi, who was sentenced to death in 2010.

CSW says other lawyers and eyewitnesses involved in the case have also received death threats.

Earlier reports suggested that Paul Bhatti was forced to flee the country. However, he informed CSW that he was fulfilling prior travel arrangements and that he would return to Pakistan to support his community there.

He said, "I have a huge community there, and I cannot leave them this way."

Pamphlets left at the scene of Shahbaz Bhatti's murder indicated that the TTP took responsibility, but nobody has been brought to justice almost three years later.

However, in September 2013, four TTP militants were arrested and charged with the murder. They are presently being tried in an anti-terrorism court in Rawalpindi.

CSW's South Asia Team Leader David Griffiths said, "There is a clear threat of vigilante justice here, and the government of Pakistan must act swiftly to provide protection for all those under threat, and ensure that the law is able to take its course.

"Shahbaz Bhatti was murdered at a time when he had no protection at all, and the threat posed by Islamist militants is real and severe.

"We therefore urge the Pakistani government to act now to avert any more tragedies, and ensure that the rule of law is upheld."