Clashes erupted between police and supporters of Nawaz Sharif in and around the twin cities of Islamabad and Rawalpindi as the government intensified its crackdown on Opposition following the return of the deposed former prime minister.

Two policemen and a worker of Sharif's Pakistan Muslim League-N were injured in an exchange of fire between police and the supporters of the leader at Attock bridge in the outskirts of Rawapindi.

Hundreds of Sharif's supporters had gathered at the bridge to enter the twin cities to greet their leader.      

Police fired tear gas shells and used batons to disperse over 200 protesters who tried to move towards the fortified airport in Islamabad, defying a government ban.

Former Pakistan President Rafiq Tarar and central spokesman of PML-N Ahsan Iqbal were among top opposition leaders arrested on Monday as they lead a procession to the Islamabad airport to welcome Sharif, witnesses said.

Iqbal was severely beaten up by the police, which clashed with a few hundred opposition activists, they said.

PML-N Chairman Raza Zafarul Haq, President Javed Hashmi and Ahsan Iqbal were among those detained on Sunday night.

"This government is anti-Islam, anti-Muslims and anti-Pakistan," Rafiq Tarar said minutes before he was taken away by in a police vehicle.

The former President said the government violated the Supreme Court verdict, which ruled that Sharif can return to the country and that the government should not create hurdles in his return.

"General Musharraf sabotaged the constitution by taking power and he has again trampled the judiciary," he said.

The chief of nationalist group Pashtoonkhwa Milli Awami Party Mehmood Khan Achakzai was also arrested       

"We will observe black day against the arrests and police violence on Tuesday," Achakzai said before he was also taken into custody.

The police also arrested Members of Parliament Tehmina Daulatana and Memona Hashmi, Kashmiri leader Barrister Mehmood Chaudhry and Opposition leader Mansoor Ali Khan.

Muttahida Majlis-e-Amal President Qazi Hussain Ahmed, who was ill, was placed under house arrest while the party's general secretary Maulana Fazlur Rehman was detained. MMA is part of the All Party Democratic Movement floated by Sharif two month ago.

Opposition parties have claimed that their 4,000 workers have been arrested over the last few days as the government braced for Sharif's return.

Criticising the Musharraf regime for the crackdown on Opposition, the Human Rights Watch has demanded the release of all detainees and asked Musharraf not to undermine Pakistan's legal system and allow Sharif to return.