ISLAMABAD, Pakistan (AP) - Voting started amid tight security Thursday in by-elections to fill five seats in Pakistan's federal parliament and 25 seats in provincial assemblies.

Polling in one constituency in the eastern city of Lahore has been delayed because of legal wrangling over whether former Prime Minister Nawaz Sharif is eligible to contest.

The by-elections follow national elections in February that installed a new civilian government opposed to former army strongman President Pervez Musharraf.

Most of the seats are up for grabs because the original victor won in more than one constituency and had to give up a seat.

Thursday's voting will not affect the balance of power in the 342-member National Assembly, where the Pakistan People's Party of slain ex-premier Benazir Bhutto controls 123 seats and Sharif's party holds 92 seats.