Pakistani opposition politician Imran Khan on Tuesday called on Pakistan's President Asif Ali Zardari to resign immediately to make way for free and fair elections. Khan, a retired international cricket star who captained Pakistan to world cup victory in 1992, has no seat in parliament but has helped to set the political agenda by campaigning on a ticket of reform ahead of elections, scheduled by mid-May.

"President Asif Ali Zardari should resign immediately. He cannot hold free and fair elections because he is holding two offices," Khan told a news conference in the eastern city of Lahore.

His call came after the Supreme Court issued an order for the arrest of the prime minister over corruption allegations, and as 25,000 people took part in the largest political protest in Islamabad since Zardari's government took office.

"The government should immediately announce new elections and should also announce a date for it," Khan told the news conference. "Change is not possible without holding of free and fair elections," he added.