ISLAMABAD: Pakistan must not buckle to extremism, President Asif Ali Zardari said on Thursday, a day after Taliban militants killed his government's only Christian minister for challenging a law on blasphemy towards Islam.

The assassination of Minister for Minorities Shahbaz Bhatti in broad daylight on Wednesday threatens to further destabilise the nuclear-armed US ally where many fear a strain of violent religious conservatism is becoming more mainstream in society.

Zardari said Bhatti's killing was the result of a “negative mindset and intolerance” that had led to the killing of a provincial governor in January.

Punjab governor Salman Taseer was also shot dead, by his own bodyguard, for his staunch opposition to the blasphemy law that mandates the death sentence for anyone insulting Islam.

“We have to fight this mindset and defeat them. We will not be intimidated nor will we retreat,” the official APP news agency quoted Zardari as saying.

“Such acts will not deter the government from eliminating extremism and terrorism,” he said. “Shahbaz fell victim to the negative mindset and intolerance that also took the lives of... Benazir Bhutto and Punjab Governor Salman Taseer.”

Meanwhile, Prime Minister Syed Yusuf Raza Gilani announced a three-day official mourning for Bhatti also on Thursday.

Gilani issued tough words as he ordered flags to be flown at half-mast and said security would be stepped up after Bhatti's slaying.

“Anti-state elements are making their last-ditch efforts by targeting important personalities in the country in order to fulfill their evil designs,” Gilani told his interior minister, Rehman Malik, according to a statement.

Gilani said the “government through fool-proof arrangements would safeguard the lives and properties of all citizens of the country, particularly to make sure they could play their role in the development of the country”.