Pakistan first expressed its "deep sadness" over Nizami's execution, saying his "only sin" was upholding the Constitution and laws of Pakistan.
"Pakistan is deeply saddened over the hanging of the Ameer of Jamat-e-Islami Bangladesh, Mr. Moti-ur-Rehman Nizami, for the alleged crimes committed before December, 1971," the Pakistan Foreign Office said in a statement.
"His only sin was upholding the constitution and laws of Pakistan," the statement said.
Bangladesh quickly hit back, saying the content of Pakistan's statement reaffirmed Nizami's role as a "traitor" who sided with Pakistani troops against "sovereign Bangladesh" in 1971.
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He said the content of Islamabad's statement now made it clear that Nizami was a "traitor" by being the chief of the infamous Al-Badr militia force in 1971 when he sided with the Pakistani troops with weapons even after "Independent Bangladesh's emergence on March 26, 1971 in line with the Proclamation of Independence of the Mujibnagar Government".
"Their statement proved it again that Nizami was one of them (Pakistanis)...They could have taken him to Pakistan as a citizen if they are so worried about him," Alam said.
"The execution is also unfortunate for the people of Bangladesh who had elected Mr. Nizami as their representative in the Parliament," it said.
Pakistan said that the execution was against the Tripartite Agreement of 1974, involving Pakistan, Bangladesh and India, under which the Bangladesh "decided not to proceed with the trials as an act of clemency".
Pakistani Parliament today also passed a unanimous resolution expressing "concern" and condemning Nizami's hanging.
Alam accused Pakistan of "deliberate misinterpretation" of the Tripartite Agreement, saying the treaty allowed Pakistan to take back home 195 war criminals belonging to their army under a provision that they would be tried at home on their return.
(Reopens FGN 37)
Pakistan had launched a crackdown on unarmed Bengalis on March 25, 1971, midnight while Jamaat sided with the Pakistani junta.
The Pakistani statement came two days after Dhaka summoned the Pakistani High Commissioner to Bangladesh and handed a "strongly worded" protest note over Islamabad's reaction to a Supreme Court judgement reconfirming Jamaat-e-Islami chief Nizami's death penalty.
Earlier also, Bangladesh's bilateral relations with Pakistan have been strained over Islamabad's reactions following executions of two major 1971 war crimes convicts -- Salahuddin Quader Chowdhury of BNP and Jamaat's secretary general Ali Ahsan Mohammad Mojaheed.