On Saturday, PTI described Pakistan Muslim League-Nawaz (PML-N) chief Nawaz Sharif's homecoming as a "coward fugitive's return under judicial asylum".
"The nation is ready to 'welcome' its criminal who has been 'adopted' by the state", a PTI spokesperson told reporters.
The PTI's strongly-worded statement came moments after Sharif landed in the South Asian nation from the Middle East following a four-year self-imposed exile in the United Kingdom.
He is expected to be the top campaigner for his PML-N party in the forthcoming general elections in Pakistan, which are scheduled to be held in January 2024.
Nawaz, who handed the reins of PML-N to his younger brother Shehbaz Sharif, is set to be the prime ministerial candidate of his party in the national polls.
During his time of exile in London, Shehbaz even occupied the country's top post from April 2022 to August 2023.
Nawaz, who was indicted by an anti-graft court in 2018 and awarded a 10-year sentence, fled the country after the Imran Khan-led government allowed him to travel abroad on medical grounds the following year.
Subsequently, Nawaz did not return to Pakistan to serve his sentence.
Before returning to Pakistan, Nawaz got major reprieves from Pakistan courts that have granted him protection from arrest in the country.