Muttahida Qaumi Movement (MQM) chief Altaf Hussain was the first to condemn Hasan's statement and he was followed by Pakistan People's Party leader Bilawal Bhutto Zardari.
Mehsud was killed with other militants when a US drone targeted a compound in the lawless North Waziristan region on Friday.
In a statement, Hussain said "every child in Pakistan" knows that 7,000 security personnel and over 40,000 citizens, including clerics and religious scholars, have been killed by the Taliban.
Earlier, PPP leader Bilawal Bhutto Zardari criticised Hasan and the Jamaat-e-Islami in a message posted on Twitter
"(Jamaat-e-Islami) proving once again they were always anti-PK & still (are) anti-PK by declaring (Mehsud) shaheed. Some1 shld do 2 'em wht Bangladesh did w/ their JI," he tweeted.
The Jamaat-e-Islami chief said yesterday that Mehsud was a martyr and asked the Taliban to carry on talks with the government.