Pakistan has hanged the former police bodyguard who shot dead Punjab's governor over his opposition to blasphemy laws, officials say.

Mumtaz Qadri shot dead Salman Taseer in Islamabad in 2011, a high profile murder that shocked the country.

But he was hailed as a hero by some Islamist groups and thousands of hardline activists protested to show their support for Qadri at the time.

Security forces have been put on alert following the execution.

Prison officials said Qadri was executed at 04:35 local time at Adiala jail in Rawalpindi, near the capital Islamabad. Just hours afterwards, angry supporters took to the streets to denounce the execution.

News agency AFP reports a heavy police presence, including riot police, in the area around Qadri's home in Islamabad.

'Religious duty'

Qadri, who had trained as an elite police commando and was assigned to Taseer as his bodyguard, shot the politician in broad daylight at an Islamabad market in January 2011. He was sentenced to death later that year.

He claimed that it was his religious duty to kill Taseer.

The case rocked Pakistan which has seen Islamist groups grow in influence in recent years.

Qadri was lauded by religious conservatives, and in his first court appearance was showered with rose petals by supporters.

Blasphemy is an extremely sensitive issue in Pakistan and critics argue that the country's blasphemy laws are often misused to settle personal scores and unfairly target minorities.

Who was Salman Taseer?

--The 2011 murder of Taseer, who was the governor of Punjab, was one of Pakistan's most high-profile assassinations.

--He was one of the most prominent liberal politicians in the country and a close associate of Asif Ali Zardari, who was then the president.

--Known to be an outspoken critic of the country's harsh blasphemy laws, arguing that they discriminated against religious minorities, and sought liberal reforms.

--He had called for a pardon for Asia Bibi, a Christian woman who was sentenced to death in 2010 for insulting the Prophet Muhammad.