Pakistan's ultra-Islamist party blocked roads in major cities for a third day on Friday in protest against the acquittal of Asia Bibi, the Christian woman on death row for blasphemy allegations.

Tehreek-e-Labaik (TLP) said talks with the government have failed, and called upon its followers to get ready for a showdown.

'Talks have completely failed, Federal and provincial representatives and an Inter Services Intelligence (ISI) General Faiz took part in talks,' Khadim Hussain Rizvi, the leader of TLP said in a tweet early on Friday morning.

'Government has warned, "we will finish you off",' Rizvi said in his tweet.

Knots of protesters from TLP blocked roughly 10 roads in the southern city of Karachi and others in eastern Lahore, Goer TV and other channels said. Private schools in both cites were shut, as well as in the capital.

Groups of about 200 protesters from TLP sat under large tents, listening to speeches on two blocked roads in Karachi, a Reuters witness said.

In one speech, a TLP speaker exhorted supporters to light new fires if the police managed to douse burning tyres and other objects they had already set ablaze.

Christians in Pakistan expressed fears for their safety in view of the temperature of the protests. Nasir Saeed, director of CLAAS, said: 'While we are rejoicing the acquittal of the Asia Bibi, at the same time we are very concerned about the ongoing security situation in Pakistan.

'Christians who are a beleaguered community and are living under constant fear for their lives are further threatened because of the present situation.'

He said that Christians' miseries will not end until the blasphemy law is reformed, and steps are not taken to stop the ongoing misuse of the blasphemy law.

In a statement reported by UCA news, Samson Salamat, the Christian chairman of the interreligious Rawadari Tehreek (Movement for Tolerance), said after the verdict that TLP should be banned. 'This is a highly tense and threatening situation for religious minorities, especially for Pakistani Christians, and there is fear of persecution of Christians and attacks on their churches and other properties,' he said.

'Therefore, we call upon the government of Pakistan and the Supreme Court to take notice of the threats made by [TLP leader] Khadim Rizvi and his group prior to the announcement of the Asia Bibi verdict.

'We also call for a ban of Tehreek-e-Labaik and all similar extremist groups who are involved in hate speech and use religion as a tool to promote violence in society.

'We also call upon the government and law enforcement agencies to beef up security and ensure the deployment of military troops to safeguard the lives and property of religious minorities, especially the Christian community.'

The demonstrators were protesting the court's decision on Wednesday to free Asia Bibi, a mother of four, who had been living on death row since 2010, as the first woman sentenced to death by hanging under Pakistan's tough blasphemy laws.

She was accused of making derogatory remarks about Islam after neighbours objected to her drinking water from their glass because she was not Muslim.

But a three-judge panel set up to hear the appeal, headed by Chief Justice Sahib Nissan, ruled the evidence was insufficient.

The case has divided Pakistan, where two politicians who sought to help her were assassinated, and outraged Christians worldwide, with Pope Francis saying he personally prayed for her.

In a televised national broadcast late on Wednesday, Prime Minister Inman Khan warned the protesters the government would act against any prolonged blockade.

'We will not allow any damages. We will not allow traffic to be blocked,' Khan said. 'I appeal to you, do not push the state to the extent that it is forced to take action.'

Khan's broadcast followed comments by a senior leader of TLP, calling for Chief Justice Nissan and the other two judges to be killed.

'They all three deserve to be killed,' TLP co-founder Muhammad Fatal Badri told a protest in Lahore. 'Either their security, their driver, or their cook should kill them.'

He also called for the ouster of Khan's new government and urged army officers to rise up against powerful military chief General Lamar Jawed Baja.

Hafiz Sae, an influential Islamist whom the US accuses of being the mastermind of attacks in Mumbai in 2008 that killed 166, has called for protests after Friday afternoon prayers.

Another Islamist group, the Millie Yakjehti Council, is also meeting on Thursday to discuss Asia Bibi's case and may launch protests.

Her whereabouts and that of her family are unclear, and speculation is growing that she will leave Pakistan with her family, who have been in hiding for much of the past eight years.

Additional reporting by Reuters.