Rehman made the remarks when he was asked by reporters outside parliament whether Mehsud, killed in a US drone strike on Friday, was a martyr.
He is not the only politician to have called Mehsud, blamed for the death of thousands of Pakistanis, a martyr. Jamaat-e-Islami chief Munawar Hasan's also called him a martyr.
Hasan's remarks were criticised by the secular-leaning Pakistan People's Party and Muttahida Qaumi Movement (MQM).
US drone attacks are an emotional issue and public opinion has been further divided with the latest strike that killed Mehsud. Addressing a cabinet meeting last night, Prime Minister Nawaz Sharif said the drone strike had done "serious damage" to his government's efforts to hold talks with militants.
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Except for a handful of politicians, most Pakistani leaders have criticised the strike, saying it was deliberately carried out to scuttle the peace talks.
However, security analysts and former military officers are happy that Pakistan's enemy number one was killed.