A day after PPP Chairman Bilawal Bhutto-Zardari called the National Accountability Bureau (NAB) the product of a “black law”, the anti-graft watchdog on Tuesday issued a statement saying the use of "foul language and threats" against NAB by the head of a political party would not deter its legal process.

At a press conference on Monday, Bilawal had announced that he would not appear before NAB on December 24, saying the call-up notice served to him by the accountability watchdog was "unconstitutional and illegal".

In a press release issued in response to Bilawal's presser, the bureau said: "NAB is an institution that works under the law of the land to eliminate corruption from the country and believes in recording the statement of a relevant person as per the law during an investigation so the person is not deprived of their legal right and all legal requisites of justice are fulfilled."

The NAB statement also said that certain media reports that Bilawal will not appear before the bureau were contrary to the assurance given by the PPP chairperson to NAB.

According to the press release, Bilawal in a letter written through his counsel had requested NAB Rawalpindi to summon him after January 15, 2020.

Later in the day, the PPP issued a statement refuting the NAB statement. Bilawal's spokesman Senator Mustafa Nawaz Khokhar said the NAB statement was contrary to the facts and that there was "no contradiction" between Bilawal's letter to NAB and his press conference.

"NAB cannot restore its lost credibility through such misleading statements," said Khokhar.

He claimed that Bilawal's lawyers in their letter to NAB had categorically termed the call-up notices as "political harassment". The spokesperson added that it had already been mentioned in the letter that despite his reservations Bilawal was ready to appear before NAB after January 15.