Pakistan Opposition Leader Calls for Tax Boycott in Anti-Gov't Protest

"After two days ... your time is up," Khan shouted to thousands of supporters at a rally in central Islamabad.

Police estimated that around 55,000 people have occupied two streets in the center of the Pakistani capital as part of separate protests led by Khan and cleric Tahir ul-Qadri, Reuters reported.

Both men say they will stay in the streets until Prime Minister Nawaz Sharif, whom they condemn as corrupt, resigns. Qadri gave him a 48-hour ultimatum on Saturday night.

Sharif's landslide election win marked the first democratic transfer of power in the history of the nuclear-armed nation of 180 million people. But barely a year after taking power, hehas struggled to overcome daily power cuts, a sluggish economy and a Taliban insurgency. Anti-Western militant groups have been growing in strength, worrying Pakistan's allies.

Khan, a former international cricket star, did not repeat a call for protesters to march on parliament, saying he did not want to provoke violence.

"We will go for civil disobedience and will not pay taxes or utility bills till the time Nawaz Sharif resigns," he said.

Less than one percent of Pakistanis pay income tax, and the last time Pakistan prosecuted someone for income tax evasion was more than 25 years ago.

Khan alternated between urging his supporters to protest peacefully and warning authorities he might not be able to control them.

"After two days I will tell (Prime Minister) Nawaz Sharif that I will not be able hold the people back," Khan said.

Khan said on Saturday that he was struggling to hold his supporters back from marching on the "Red Zone", an enclave that is home to top government buildings like Parliament and the Supreme Court and most Western embassies.

Many of the young men at Khan's protest said they were eager to push against the fortified lines of riot police if Khan commanded.