Police said Asif Ali Zardari had not been arrested after his plane from Dubai landed on Saturday in the eastern city of Lahore and that he would be taken to his residence in the city and then freed.
"He has not been arrested. We have just shifted him to his house," Superintendent of Police Mohammad Usman said. "He will be free there."
However, witnesses said police had erected barricades around Zardari's house in an upmarket neighbourhood in Lahore to prevent supporters or journalists from reaching it.
Police block roads
Zardari, who was released on bail from eight years in jail late last year, was returning to Pakistan for the first time since travelling to visit his wife in Dubai in December.
Hundreds of police were deployed to block roads to the airport to prevent opposition supporters gathering there and used batons to disperse about 50 who managed to evade the cordon.
The Geo TV channel, which had a correspondent travelling on the DC-9 airliner belonging to private Pakistani airline Aero Asia, said police boarded it after it landed.
It said among those detained were Makhdoom Amin Fahim, leader of the parliamentary wing of Bhutto's Pakistan Peoples Party (PPP), and its former foreign minister Sardar Asseff Ahmed Ali.
The government of military ruler President Pervez Musharraf refused to give permission for PPP supporters to rally in Lahore to greet him, and the party says thousands of its activists have been detained in the past week.
Information Minister Shaikh Rashid Ahmed said Zardari's movements would not be restricted. "He is free and independent and can go anywhere in the country. All those detained will be freed soon," he said.
PPP activists were arrested to
prevent a planned rally
On Friday, Zardari vowed "street agitation" if the government tried to block a rally by supporters to welcome him home.
"We don't want confrontation with the government," he said. "But they have created a situation under which we have no other option but to launch street agitation.
"We will launch a movement to fill jails," he added.
The crackdown has again dimmed hopes of reconciliation between Musharraf, who seized power in a coup in 1999, and Bhutto, prime minister for two terms in the 1980s and 1990s.
Bhutto has lived in self-imposed exile for fear of arrest on corruption charges since 1999, and Musharraf in the past has said she would not be allowed to return to politics.
Apparently seeking to bolster his power base and respond to Western critics pushing him to lift curbs on democracy, Musharraf appeared to soften his position towards her in recent months.
"We will launch a movement to fill jails"
Asif Ali Zardari,
husband of former premier Benazir Bhutto
However, while Zardari's release in November, despite still-pending charges ranging from corruption to murder, raised speculation that Musharraf was trying to improve relations, authorities then blocked his attempts to rally supporters.
In a similar incident in December, police boarded an airliner that had brought Zardari to Islamabad, detained him and flew him back to Karachi to prevent him from addressing rallies.
In an interview with Reuters on Thursday, Musharraf said it was important for moderate forces to unite against extremism and that he would be willing to meet Bhutto one day. But he said rallies to welcome Zardari would not help reconciliation.