A Pakistani court has sentenced six men to death for the mob slaying of a Sri Lankan factory manager accused of blasphemy.

A judge in the city of Gujranwala announced the verdict on April 18 after a secret trial that took about a month inside a prison compound, public prosecutor Nadeem Sarwar said.

At least nine men were handed life terms for aiding the murder, while another 72 were given two years in jail each, Sarwar said.

The fatal attack on clothing factory manager Priyantha Kumara in the eastern town of Sialkot on December 3 caused outrage in the Muslim-majority nation and drew global condemnation.

A mob of around 100 men bludgeoned Kumara to death after accusing him of tearing a poster with text from the Koran written on it. They later burned Kumara’s body.

Several gruesome video clips shared on social media showed a mob beating the victim while chanting slogans against blasphemy. Other clips showed the victim’s body set ablaze.

Sarwar said the perpetrators were identified in the videos, which they recorded themselves on mobile phones and uploaded on social media.

Hafiz Israr ul Haq, a lawyer for one of the men sentenced to death, called the verdict unfair.

"This was a case of mob violence and in such cases, no individual's role can be ascertained with certainty," he told AFP.

The men will have two chances to appeal.

Blasphemy is an explosive issue in Pakistan, where even the slightest suggestion of an insult to Islam can spark violence. Many people accused of blasphemy are killed by mobs before they even get to trial.

Pakistan’s blasphemy laws allow a death sentence for anything deemed insulting to Islam or the Muslim Prophet Muhammad, but rights activists say they are often used against religious minorities or in personal vendettas.