Pakistan's deposed premier Nawaz Sharif on Sunday staged a political comeback by criticising the powerful Army and said the Opposition was not against Prime Minister Imran Khan but against those who brought an "inefficient" man to power.

Addressing the All-Parties Conference (APC) hosted by the Pakistan Peoples Party (PPP) via a video link aimed at launching a protest movement against the Khan-led Pakistan Tehreek-e-Insaf (PTI) government, the three-time premier launched a scathing attack on the ruling party for its failure to address the basic problems of the people .

Sharif, 70, the Pakistan Muslim League Nawaz (PML-N) supremo, has been living in London since November last year after the Lahore High Court granted him permission to go abroad for four weeks for treatment.

On Friday, PPP chairman Zardari talked to him over phone and invited him to virtually attend the Opposition-led All Parties Conference (APC) scheduled to be held on Sunday.

Addressing the conference, Sharif criticised the country's powerful establishment for allegedly supporting Khan.

"Our struggle is not against Imran Khan. Today, our struggle is against those who installed Imran Khan and who manipulated elections (of 2018) to bring an inefficient man like him into power and thus destroyed the country, he said.

Sharif said that the foremost priority should be to remove this selected government and this system , adding that "if the change is not brought, it will bring irreversible loss to this country.

He asked the powerful Army to stay away from politics and follow the Constitution and vision of the country's father Quaid-e-Azam' Muhammad Ali Jinnah.

It is very important that our armed forces stay away from our governmental system according to our Constitution and the Quaid's speech, and not interfere with the people's choice. We have made this country a joke in our own eyes and internationally as well, he said.

Sharif pointed out that former prime minister Yusuf Raza Gilani once said that there was "a state within a state" in Pakistan.

It is saddening that the situation has escalated to a state above the state. This parallel government illness is the root-cause of our problems, he said.

He asked the leaders attending the conference to make important decisions to change the system of the country, alleging that the current government has enforced martial law in the country.

This conference should bring forth a concrete plan of action for saving democracy, a concrete policy should be made for solving the problem of a parallel state I again urge this all-party conference to go beyond its traditional ways and form a plan of action, he said.

Sharif reiterated that the vote of people should be honoured which was the only way to save democracy and the country.

"Pakistan has been constantly deprived from a democratic system. When the vote is dishonored, the entire democratic system becomes meaningless. When it is decided before the election process as to who will win and who will lose, then it can be guessed how the public is betrayed and how the public's mandate is stolen, he said.

He said that military dictators ruled for multiple years but none of the elected prime ministers had been allowed to complete the allotted five years.

Without naming former military dictator Pervez Musharraf, he said that the court did not act against him for suspending the Constitution.

Courts gave dictators the right to play with the Constitution and acquitted someone (Musharraf) who suspended the Constitution twice. Whereas the ones who follow the Constitution are still in jail, he said.

The powerful Army, which has ruled Pakistan for more than half of its 70 plus years of existence, has hitherto wielded considerable power in the matters of security and foreign policy.

Before Sharif, former president Asif Ali Zardari also addressed the conference through a video-link and criticised the government which he said was using the tactics to suppress the Opposition.

It is important that all parties join hands to get rid of this government, he said.

PPP chairman Bilawal is hosting and presiding over the conference with several opposition parties attending it to chalk out a course of action to launch protests against the government.

Sharif, his daughter Maryam and son-in-law Muhammad Safdar were convicted in the Avenfield properties case on July 6, 2018.

Sharif, who was deposed in 2017, was also sentenced to seven years in the Al-Azizia Steel Mills case in December 2018. But, he was bailed out in both cases and also allowed to go to London for medical treatment.

He was given eight weeks to return but failed to come back due to health complications, according to his lawyer.