MULTAN- As twin protests in Islamabad entered a fifth day today, police arrested some 150 supporters of protest leaders overnight in Punjab province in a crackdown ahead of widening demonstrations in the capital.

Opposition leader Imran Khan and firebrand cleric Tahirul Qadri have led tens of thousands of supporters from Punjab to Islamabad in a bid to bring down Prime Minister Nawaz Sharif, whom they accuse of rigging elections and corruption.

The protests have piled extra pressure on the 15-month-old civilian government already struggling to overcome high unemployment, daily power cuts and a Taliban insurgency.

The protests have raised questions over the political stability of Pakistan, a nuclear-armed nation of 180 million people with a history of coups.

Police in Punjab, Pakistan's wealthiest and most populous province, arrested 147 supporters of Khan and Qadri overnight to prevent them joining the protests in Islamabad, said Inspector Rana Hussain in the central town of Sargodha.

Khan said that he would lead protesters into the capital's "Red Zone", an area home to Western embassies and key government ministries.