Sharif and his League were part of the coalition government, together with the majority Pakistan Peoples Party of Asif Ali Zardari, widower of former prime minister Benazir Bhutto.
The two parties, which collaborated in the removal of President Musharraf, had clashed over various questions, from the selection of the former president's successor to the restoration of judges removed by Musharraf.
According to local analysts, the withdrawal of League N should not lead immediately to the calling of new elections, because the Peoples Party is thought to be capable of guaranteeing the majority necessary to carry the government forward.