Islamabad: Gunmen shot dead Pakistan's only Christian government minister on Wednesday for challenging a law that mandates the death penalty for insulting Islam, the second top official killed this year over the blasphemy law.

The assassination of Shahbaz Bhatti, minister for minorities, is the latest sign of deep political instability in the nuclear-armed U.S. ally.

Frequent militant attacks and chronic economic problems have raised fears for Pakistan's future. Pakistani Taliban militants claimed responsibility for killing Bhatti, with a Taliban spokesman saying the minister was a blasphemer.

Bhatti was shot in broad daylight while traveling in a car near a market in the capital, Islamabad, police said.

"The attackers were wearing shawls and opened indiscriminate fire as they got close to the minister's car," Islamabad police chief Wajid Durrani told reporters.

The windshield of Bhatti's car had four or five bullet holes and blood covered the back seat. A hospital spokesman said Bhatti, who had spoken out against the anti-blasphemy law, received several wounds.

The law has been in the spotlight since last November, when a court sentenced a Christian mother of four to death.

On January 4, the governor of the most populous province of Punjab, Salman Taseer, who had strongly opposed the law and sought a presidential pardon for the 45-year-old Christian farmhand, was killed by one of his bodyguards who had been angered by the governor's stand.

Bhatti was traveling without security, having left two police escorts at home, Durrani said.

"There was no protection when he left the house," the police chief said. "There was just a private driver with him. We don't know about the minister's thinking, but we had provided him two escorts because he was under threat."

Al Qaeda-linked Pakistani Taliban militants, fighting to bring down the state, had called for Bhatti's death because of his attempts to amend the law. A militant spokesman, Sajjad Mohmand, said they had killed him.

"He was a blasphemer like Salman Taseer," Mohmand said by telephone from an undisclosed location.

Prime Minister Yusuf Raza Gilani condemned the killing and ordering the Ministry of Interior to investigate.

"PROTECTION FROM HEAVEN"

Last month, in an interview with the Christian Post, Bhatti said he had received threats. "I received a call from the Taliban commander and he said, 'If you will bring any changes in the blasphemy law and speak on this issue, then you will be killed'," Bhatti told the newspaper.

"I don't believe that bodyguards can save me after the assassination (of Salman Taseer). I believe in the protection from heaven."

The January killing of Taseer was widely praised by hardline Islamist groups such as the Jamaat-e-Islami (JI), the country's largest religious party.

But the party denounced Bhatti's murder.

"We condemn this killing. This is a conspiracy and it may be an attempt to divert attention from the case of Raymond Davis," senior JI leader Farid Paracha told Reuters.

Davis is an American CIA contractor on trial for killing two Pakistanis. The case has been taken up by religious parties which have called for Davis to be hanged.

Bhatti's killing is likely to further deter any attempt to change the blasphemy law that mandates death for anyone who speaks ill of Islam's Prophet Mohammad.

Sherry Rehman, a former government minister and member of the ruling Pakistan People's Party, of which Bhatti was also a member, tried to change the law last year but the party leadership forced her to stop in the face of opposition.

The Anglican Church, the Archbishop of Canterbury, Rowan Williams, and the Archbishop of York, John Sentamu, condemned the murder and the impact it would have on Pakistan's religious minorities.

"This further instance of sectarian bigotry and violence will increase anxiety worldwide about the security of Christians and other religious minorities in Pakistan," they said in a statement.

The law has its roots in 19th Century colonial legislation to protect places of worship, but it was during the military dictatorship of General Mohammad Zia ul-Haq in the 1980s that it acquired teeth as part of a drive to Islamise the state.

Liberal Pakistanis and rights groups believe the law to be dangerously discriminatory against tiny minority groups.

Under the law, anyone who speaks ill of Islam and the Prophet Mohammad commits a crime and faces the death penalty, but activists say the vague terminology has led to its misuse.

Christians who make up about two percent of the population have been especially concerned, saying the law offers them no protection. Convictions hinge on witness testimony and often these are linked to personal vendettas, critics say.

Security analyst Imtiaz Gul says the law was open to abuse by people settling scores.

"We would hope this forces the government or the parliament to take action," he said. "They should somehow improve the blasphemy law."

Convictions are common although the death sentence has never been carried out. Most convictions are thrown out on appeal, but mobs have killed many people accused of blasphemy.