LAHORE, Pakistan (Reuters) - Pakistani police said they arrested 150 hardline Muslim activists on Wednesday as they tried to rally in support of the country’s tough blasphemy law on the anniversary of a provincial governor’s assassination over his call to reform the statute.

A supporter of the Ahle Sunnat religious political group holds a sign in support of convicted killer Mumtaz Qadri during a sit-in protest demanding his release in Karachi, Pakistan November 20, 2015. In 2011, Salman Taseer, the governor of Punjab, was shot dead by a bodyguard, Mumtaz Qadri, after he had sought a presidential pardon for Asia Bibi, a Christian woman accused of blasphemy. REUTERS/Athar Hussain

Security was tight in the eastern city of Lahore throughout the day. Police barricaded many parts of Lahore to prevent demonstrators from gathering, causing massive traffic jams.

Lahore Deputy Inspector General of Police Haider Ashraf said the arrested activists belonged to Tehreek-i-Labaik Ya Rasool Allah, a coalition of Islamist groups who were planning to attack people staging a vigil to commemorate the anniversary of the governor’s killing.

Tehreek-i-Labaik Ya Rasool Allah could not be reached for comment.

Punjab Governor Salman Taseer was gunned down by his bodyguard Mumtaz Qadri six years ago for championing the case of a Christian woman who was sentenced to death under the blasphemy law, which he said needed to be reformed.

Last February, Pakistan executed Taseer’s killer, but tens of thousands of supporters turned up at his funeral and hailed him as a hero of Islam.

“When police received reports that the Labaik Ya Rasool Allah Movement planned to attack the gathering, we reacted preemptively and cordoned off the area,” Ashraf told Reuters.

“The activists threw stones at police, who retaliated with baton charge and arrested 150 members.”

Ashraf said those arrested were booked for disrupting law and order and assaulting police. The head of the Labaik group, Maulana Khadim Hussain Rizvi, was also among those detained.

Earlier this week, the hardline Islamist group Sunni Tehreek said it was demanding police in Lahore charge Shaan Taseer, the son of the slain governor, with blasphemy over a Christmas message calling for prayers for those charged under the law.

Taseer told Reuters on Monday that he had received “very credible death threats” from supporters of the hardline Muslim philosophy that inspired his father’s killer, bodyguard Mumtaz Qadri.

Controversy over the blasphemy law has exposed the growing gap between hard-line religious conservatives and liberals in the South Asian country.

More than 100 people are charged with blasphemy and jailed each year in predominantly Muslim Pakistan, many of them Christians and other minorities. Critics say the law is often invoked in cases of personal disputes.

No one has yet been executed, but at least 65 people have been murdered in connection with blasphemy allegations since 1990, according to the Centre for Research and Security Studies and a Reuters tally.