Lahore, Jan 05 (Agencies): Thousands of Pakistani police were on high alert in Lahore on Wednesday ahead of the funeral for an outspoken provincial Governor shot dead by a bodyguard.

Punjab Governor Salman Taseer, a high-profile, 66-year-old businessman and media tycoon, was a stalwart of the ruling Pakistan People's Party, and his assassination on Tuesday sent nuclear-armed Pakistan reeling at a time of great political turmoil.

Taseer, regarded as a moderate voice in a country increasingly beset by zealotry, was a close ally of US-backed President Asif Ali Zardari.

He is the highest-profile Pakistani political figure to be assassinated since former Prime Minister Benazir Bhutto was slain three years ago, and his death underscores the growing danger in this country to those who dare to challenge the demands of Islamist extremists.

"Police are on maximum alert. Police are guarding all important installations in the city," said Khusro Pervez, the commissioner of Lahore.

Thousands of police were guarding Taseer's residence and other key sites.

An intelligence official who interrogated the suspect, Mumtaz Qadri, said the 26-year-old commando had been planning the assassination since learning four days ago that he would be deployed with the Governor.

Qadri was arrested immediately after the shooting but it wasn't immediately clear on Wednesday whether he had been officially charged with a crime.

Political allies questioned why Taseer hadn't been better protected, given the weeks of angry protests outside the Governor's mansion over his opposition to the blasphemy laws.

Prime Minister Yousuf Raza Gilani announced a three-day period of national mourning and ordered flags lowered to half-staff.

Joining international condemnation of the assassination, US Secretary of State Hillary Rodham Clinton said, "I had the opportunity to meet Governor Taseer in Pakistan and I admired his work to promote tolerance and the education of Pakistan's future generations."

PPP leaders and supporters gathered at the house on Wednesday ahead of the funeral.

Authorities had installed walkthrough metal detectors at the house as an added security measure for the funeral.

Taseer's admirers called the Governor a courageous opponent of Pakistan's shift in recent years away from South Asia's Sufi-influenced moderation to the more fundamentalist approaches to Islam found in some areas of the Middle East.

His death also came as a blow to the ruling PPP, which is struggling to retain power after the defection of a key ally from its governing coalition.

The country's leading Opposition party, Pakistan Muslim League-N, on Tuesday gave the Government a three-day deadline to accept a list of demands to avert a no-confidence vote that could result in the government's collapse.

But PML-N spokesman Sadiqul Farooq spokesman said on Wednesday that that deadline had been extended by three days because of Taseer's assassionation.

Overnight, Interior Minister Rehman Malik, a PPP member and friend of Taseer, visited the bloodied Islamabad street where the murder occurred and faulted guards for not surrounding Taseer as he left the restaurant.

PPP senior leader Jehangir Badar demanded a thorough probe into the circumstances of the murder and called for calm.

Police were trying to determine how Qadri was assigned to Taseer's security detail on Tuesday and whether he'd had any help.