The funeral of the Punjab Province governor, assassinated Tuesday by one of his security guards, has taken place under tight security in the Pakistani city of Lahore.

Salman Taseer was buried Tuesday in a state funeral held at the Governor's House. Police patrolled the streets and guarded key sites around the city.

Taseer was shot to death Tuesday in Islamabad. The suspect, identified as Mumtaz Qadri, confessed to killing the governor because of his opposition to controversial Islamic blasphemy laws.

Pakistani Interior Minister Rehman Malik said an investigation is underway to determine whether the killer acted alone or as part of a wider organization.

The assassination came as the ruling Pakistani People's Party, of which Taseer was a member, struggles to form a new government following the defection of a key coalition partner.

The leading opposition party, headed by former Prime Minister Nawaz Sharif, had given the government three days to agree to a series of reforms in order to avoid collapse. But the party pushed its deadline back until after the mourning period for the Punjab governor.

Taseer, a staunchly secular and progressive politician, was an outspoken opponent of religious extremism. He publicly led a charge to reform a blasphemy law that set harsh penalties for offenders. He recently called for the release of a Christian woman condemned to death for allegedly making derogatory remarks about the Prophet Muhammad.

U.S. Secretary of State Hillary Clinton called Taseer's death "a great loss" and said Washington remains committed to helping the government achieve peace and stability.

Taseer's killing is the most high-profile political assassination in Pakistan since former Prime Minister Benazir Bhutto was killed three years ago.