In a meeting with PPP ticket-holders of Punjab province at his private residence in Lahore, Zardari claimed some "international forces" did not want the party to come to power again.
"These forces were not happy with the (outgoing) PPP government's agreements with the countries in the region," he said.
PPP leaders believe that the United States was not happy over the previous government's agreements for a gas pipeline and the management of GwadarPort with Iran and China, respectively.
Zardari said the mandate of the PPP had been "stolen" but it would play an effective role at the centre as an opposition party.
He said he would actively participate in politics after completing his tenure as President in September.
The losing PPP candidates spoke out against former premiers Gilani and Ashraf and former Interior Minister Rehman Malik, saying they had caused irreparable harm to the party.
"The poor governance of Gilani and the mishandling of the energy crisis by Ashraf cost us dearly in the May 11 polls," a PPP candidate, who lost in central Punjab, told PTI.
Another PPP activist, who did not want to be named, criticised the party's decision of "wasting" about Rs 300 billion on the Benazir Income Support Programme instead of addressing the energy crisis by clearing a circular debt of Rs 400 billion.
Image: Asif Ali Zardari
Photograph: Ray Stubblebine/Reuters
I should have quit presidency to lead PPP: Zardari
Guns are no solution, talks a better option: Sharif
Kashmir is no more a vote puller in Pakistan
Chinese Premier to meet Sharif during Pakistan visit
Pakistanis vote in historic polls, 24 killed in violence