Former Prime Minister Nawaz Sharif arrived in Pakistan on Monday after years of exile to try to challenge the rule of Gen Pervez Musharraf who toppled him in a coup in 1999.
Before his departure from London he said he aimed to "take Pakistan back to the rule of democracy".
Mr Sharif's supporters were in high spirits before his arrival, especially in his heartland of Punjab province.
But security forces put on a show of force, surrounding Islamabad airport. Earlier many of Mr Sharif's party colleagues were arrested. Police fired tear gas at demonstrators.
Mr Sharif, who says he is determined to contest elections later in the year, waved as he arrived in Pakistan after an eight-year exile.
But his return was short-lived. He was arrested by the authorities as he stepped off the plane, charged with money-laundering and promptly put on a plane to Saudi Arabia.
More demonstrators were rounded up while Mr Sharif's fate was being decided at Islamabad airport.
The other main contender for power, former Prime Minister Benazir Bhutto, has said that she will announce on Friday what her plans are to return to Pakistan too.