Voting begins in Pakistan presidential election

ISLAMABAD, Pakistan (CNN) - Members of Pakistan's parliament began voting Saturday to elect a new president. Security around the National Assembly building in Islamabad was tight, with police on the roof and at the gates and riot police on site.

The frontrunner in the race is the pro-American widower of former Pakistani Prime Minister Benazir Bhutto, who was assassinated late last year. Asif Ali Zardari, 53, took over Bhutto's Pakistan People's Party (PPP) after her death.

Under Pakistan's constitution, the president is elected by a majority vote of the two houses of the National Assembly and the four provincial assemblies around the country.

Whoever wins will rule a nuclear power threatened by Islamic militancy and economic turmoil. The Taliban are resurgent in Pakistan and the country's economy is tanking.