Opponents of Sharif gathered on Thursday for two separate marches from Lahore; one by supporters of former cricket star-turned politician Imran Khan and the other by followers of the Pakistani-Canadian cleric Tahirul Qadri.

Riot police sealed off access to the capital, Islamabad, with barbed wire and shipping containers. More than a dozen protesters and at least three policemen were said to have been killed in violence ahead of the anticipated march, on the eve of the anniversary of Pakistani Independence.

While the mood around the Khan camp was festive, with protesters chanting and listening to music, supporters of Qadri - who has vowed to overthrow the government by the end of this month - were said to be more subdued.

Qadri, who is in control of a network of religious schools and charities has met with strong opposition from the government.

The crowd outside Qadri's home was surrounded by police, who blockaded the would-be marchers with containers. In contrast, a late night court ruling on Wednesday suggested that the pro-Khan march might be given the official go-ahead.

Analysts have said the government has adopted the differing approaches to the protests in a strategy to divide the two groups. It is thought that the reaction to the protests by the army, which has ruled Pakistan for more than half of the country's history since independence in 1947, may prove pivotal in Sharif's chances of retaining power.

Khan is calling for Sharif, citing irregularities in the May 2013 election, of which Khan was declared the outright winner. Qadri, meanwhile is demanding changes to the electoral system, which he claims is undemocratic.

rc/kms (dpa, Reuters)