PTI leader Fawad Chaudhry on Thursday said "threatening calls" from "unknown numbers" should stop hours after PTI leaders claimed a pilot flying party chairman Imran Khan to his rallies had received them.

Imran has embarked on a whirlwind campaign ahead of the by-elections in Punjab. From July 7-15, he is expected to address dozens of public gatherings. He has also held several in the past few weeks.

On Tuesday, he had fired off a warning that he would be forced to "reveal everything" about the characters involved in the alleged conspiracy to oust his government if harassment of him and his party did not cease.

Addressing a press conference in Islamabad today, PTI leader Fawad Chaudhry alleged that "threatening calls" were being made, adding that Imran's pilots were receiving calls from "unknown numbers".

He also played a clip of the alleged call, holding his mobile phone close to the microphones on the table where he was sitting and terming the development as "unfortunate".

In the clip Fawad played, a male voice can be heard asking the receiver of the call to delete what is presumably a social media post. "You will be picked up by 5pm tomorrow," the unknown caller can be heard saying.

Fawad reiterated that this was "unfortunate", expressing the hope that the relevant authorities would investigate this.

"There are only two big [security] agencies," he said. Fawad said that recently, Chief of Army Staff Qamar Javed Bajwa and the "DGI" had issued orders for their institutions to stay away from "such matters".

"I am hopeful these directives will be implemented. If people from the Intelligence Bureau (IB) are doing this, then I would urge their head to look at their institution."

He alleged that "calls from unknown numbers are made by two institutions".

"These calls from unknown numbers should stop. People have the azadi of free will.

"Fear doesn't last forever," the former information minister said, adding that "Pakistan is not Burma".

He noted that martial law had been imposed in the country four times but had also subsequently ended.

"If you think you can rule over Pakistan on the basis of power, this doesn't happen here. There will be retaliation, the people will stand up."

Fawad said that the "current peace" should be allowed to prevail, adding that holding early elections was the only way to rid the country of political instability.

Earlier in the day, Asad Umar had claimed that the pilot flying Imran to his rallies was receiving phone calls and "being given threats".

"How low will they sink," he asked, without specifying who he was referring to.

In another tweet, he shared a poem by Martin Niemöller — a prominent Lutheran pastor in Germany who was outspoken against Adolf Hitler.

"First they came for socialists. I did not speak. I was not a socialist. Then they came for trade unionists. I did not speak. I was not a trade unionist. Then they came for Jews. I did not speak. I was not a Jew. Then they came for me and there was no one left to speak for me."

PTI's Shahbaz Gill also made similar claims, saying: "The pilot of the plane used during Imran's rallies is receiving threatening calls from unknown numbers.

"It seems that, in your eyes, there is no limit to the use of force," he said, without elaborating further.

"You want to cross limits by using intimidation tactics but the nation is no longer afraid," he said, adding that "everything that was unknown is now known".

"If Imran's plane is damaged on the ground or in the air, then the nation should remember who is doing all this," Gill said.

First private companies were threatened over offering their planes. Attempts were made to cancel our plans after planes were deliberately made to appear as though they were not fit to fly, he claimed.