ISLAMABAD — Pakistani Christians burned tires and rallied for justice Thursday, a day after Islamist militants assassinated a Catholic government minister who had braved death threats to speak out in their defense.

The government, which has been accused of appeasing hard-liners, vowed to tackle the threat, but officials routinely make such promises after high-profile attacks and questions remain over its will to counter militants once supported by the state.

Shahbaz Bhatti, 42, was gunned down in the capital, Islamabad, apparently because he had urged Pakistan to reform harsh laws that impose the death penalty for insulting Islam. He had been given police and paramilitary guards but had asked them not to accompany him while he stayed with his mother, according to police.

Bhatti, who was minister for religious minorities, was the second Pakistani politician killed in two months over the blasphemy laws, the support of which has become a rallying cry for right-wing Islamist political parties and clerics. On Jan. 4, Punjab Gov. Salman Taseer was shot dead by a bodyguard who disagreed with his view that the laws need to be changed.

The U.S. is alarmed at Pakistan's seeming downward spiral and is supporting its government and security forces in the fight against terrorism, but ties between the two nations have been badly strained by the arrest of a CIA contractor in the eastern city of Lahore for killing two Pakistani men.

The American, Raymond Allen Davis, appeared in court Thursday but was not indicted after his lawyer, appearing at court for the first time, said more time was needed to study the charge sheet. A higher court is scheduled to rule later this month on whether Davis has diplomatic immunity, as the U.S. insists.

In Washington, State Department spokesman P.J. Crowley said the U.S. is "concerned that the proceedings are ongoing."

"We continue to stress to the Pakistani government and to the Pakistani courts that he has full immunity from criminal prosecution," Crowley told reporters.

Bhatti's killing showed yet again the challenges posed by extremists to the nuclear-armed country, which is also saddled with a stagnant economy and a corrupt political and military elite that has been unable to deliver good governance for decades.

As the government declared three days of official mourning, Christians protested in several cities. Bhatti rose to prominence defending a Christian woman sentenced to death for blasphemy.

"Anyone who commits injustice or oppression will have to answer for it," several hundred people chanted in the city of Rawalpindi near the capital as thick clouds of smoke rose from burning tires.

One woman shouted that the killers were "defaming the image of Islam and trying to demolish my country of Pakistan."

Christians make up around 5 percent of the country's 180 million people, and along with other non-Muslim minorities have been often been persecuted. They typically live in poor parts of town, separated from Muslims, and do low-skilled, badly paid jobs.

Police released a sketch of one of Bhatti's killers and said several people were being questioned in connection with the assassination, but that none apparently had direct links with the attackers.

"Our resolve to fight this menace will continue as we consider it as our own war," said Prime Minister Yusuf Raza Gilani.

Taseer's assassination shocked many in Pakistan and around the world, but the aftermath perhaps more so: extremists held public celebrations and the government, apparently afraid of the hard-liners, did not loudly condemn the attack or arrest those praising the killer.

There has been no such reaction this time around, though the government has avoided mentioning Bhatti's support for amending the blasphemy laws in its comments. Islamist parties and clerics have condemned the killing, but have tempered that by spreading conspiracy theories it was part of a foreign plot to destabilize Pakistan.

The statements have come even though pamphlets signed by al-Qaida and the Taliban were found at the scene claiming responsibility for the murder.

"I am afraid that this could be an American conspiracy to defame the government of Pakistan, Muslims and Islam," said Rafi Usmani, who bears the title of grand mufti of Pakistan.

Associated Press writers Ashraf Khan in Karachi, Khalid Tanveer in Multan, Yousaf Awan in Rawalpindi, and Bradley Klapper in Washington contributed to this report.