Islamabad - Police used tear gas and batons on the supporters of opposition leader Nawaz Sharif in Pakistan's capital Islamabad during third day of protest on Friday against a court ruling that banned him from elected office.

Hundreds of demonstrators blocked the main highway linking the capital with the adjoining city of Rawalpindi and pelted the vehicles with stones. Law enforcers fired rounds of tear gas to disperse the crowd and chased them in the nearby streets.

"We have arrested fifteen rioters," said a local police official Nisar Ahmabd. According to him the protesters also damaged the vehicle of Islamabad police chief Kalab Abbas.

The angry crowds also attacked and damaged a police station in the Shahzad Town area of the capital. Similar violent clashes were reported in other areas of the Punjab, the stronghold of Sharif's Pakistan Muslim league-Nawaz (PML-N).

Paramilitary troops were deployed in Lahore, the provincial capital of Punjab, to maintain law and order. "The Rangers were called in on the request of the Punjab government," said Interior Ministry spokesman Shahidullah Baig.

These are the large protests against the new civilian government, which came to power in last year's general elections after almost nine-year military rule.

Thousands flooded the streets Wednesday immediately after Pakistan's court upheld a verdict that barred former prime minister Sharif from contesting elections, because of a criminal conviction after his government was ousted in 1999 by the then military chief Pervez Musharraf.

The court also nullified the 2008 election of his brother Shahbaz Sharif and removed him from the post of Punjab's chief minister. The Sharif brothers have accused president Asif Ali Zardari of "ordering" the verdict.

Following the court ruling, Zardari imposed federal rule and prevented Punjab's regional assembly from holding a session, apparently in a bid to block PML-N from choosing a new chief minister.

Shahbaz Sharif addressed a rally in Lahore on Friday afternoon and asked his supporters to join the lawyer's "long-march" starting on March 12 from south-western city of Quetta and heading for the capital Islamabad.

"The existing judges will become history on March 12," he told a rally in Lahore, the provincial capital of Punjab.

The political tensions between Zardari and Sharif, the two traditional rivals who joined hands last year to form a coalition government and oust former president Musharraf, risk diverting Pakistan's focus from fighting al-Qaeda and Taliban militants entrenched in its tribal region along Afghan border. (dpa)