The National Accountability Bureau (NAB) has launched another inquiry into Opposition Leader Shahbaz Sharif regarding the alleged illegal use of the prime minister's plane during his stint as chief minister, well-placed sources in the bureau told DawnNewsTV on Tuesday.

A NAB source said that the accountability watchdog would grill Fawad Hassan Fawad, who was serving as principal secretary to then prime minister Nawaz Sharif at the time, in this regard. Fawad had granted the permission, the source alleged, adding that Shahbaz would be summoned for questioning at a later stage.

"The bureau wants to know why the then prime minister allowed the then chief minister to use his plane, and how many times such permission was granted and under which rules," the source said.

According to sources, the accountability watchdog has constituted a combined investigation team (CIT) and launched a formal probe into the allegations.

The CIT has sent a letter to PM House seeking the usage records for the plane ─ meant for the prime minister's use ─ from 2014 to 2018.

Shahbaz Sharif who is currently on bail in the Ashiana-i-Iqbal Housing Scheme and Ramzan Sugar Mills cases, is facing multiple corruption cases.