Police fired tear gas and rounded up protesters in Islamabad Friday, with the nuclear-armed nation in turmoil since a court banned the top opposition leader from contesting elections. The cabinet met to discuss the crisis and paramilitaries went on alert for potential trouble, one day after the country's marked the biggest protests yet against President Asif Ali Zardari, who took office last September. Protesters are heeding a call from former prime minister Nawaz Sharif, whose party is the second largest in the country, to rise up after the Supreme Court Wednesday barred him and his brother from holding public office. Zardari and Nawaz Sharif are at loggerheads over the future of the country, a key US ally in the fight against Taliban and Al-Qaeda militancy which has been teetering under financial crisis, Islamist extremism and weak government.