(Updates with quotes)
By Faisal Mahmood
ISLAMABAD, Aug 18 (Reuters) - Lawmakers from Pakistan's third largest party will resign from parliament to try to force Prime Minister Nawaz Sharif to step down, a party official said on Monday.
Led by former cricketer Imran Khan, Pakistan Tehreek-i-Insaaf controls 34 of the National Assembly's 342 seats.
The party will also withdraw from three out of four provincial assemblies in Pakistan, senior party official Shah Mehmood Qureshi told local television channels.
The fourth province, Khyber Pakhtunkhwa, is under PTI control and officials there will not resign, he said. Khyber Pakhtunkhwa is the heartland of the Taliban insurgency and plagued with militant violence and criminal gangs.
Khan accuses Sharif of rigging elections last year. Sharif won a landslide victory in the first democratic transfer of power in a country with a long history of coups.
Qureshi said the party was just waiting for three more lawmakers to hand their resignations to him and then he would deliver them as a group.
On Friday, Khan and fiery cleric Tahir ul-Qadri led tens of thousands of supporters into the capital to demand Sharif's resignation, vowing to camp on the streets until he stepped down. Sharif has refused to go but said he would listen to the protesters' complaints about vote-rigging and corruption. (Reporting by Faisal Mahmood; Writing by Katharine Houreld; Editing by Robin Pomeroy)