"This was not a letter, neither from presidency nor from any government organisation,"
Malik told reporters on the sidelines of an event in Islamabad. "This is communication through SMS by two individuals. One is an American national and second is our Ambassador," he said.
The information available indicated there was "an exchange of SMS and Blackberry messages", he added. "Now we have to see that who initiated these (messages).. And if his (Haqqani?s) point of view was not satisfactory, then it is clear (the matter) is open for investigation," Malik said.
Both Malik and Prime Minister Yousuf Raza Gilani said Haqqani should be given an opportunity to explain his position.
Malik said no one could be condemned without being heard.
Talking to reporters in Peshawar, Gilani said the matter of the secret memo would be taken to its "logical end" while protecting national interests though it would be "unjust and against the norms of justice to jump to conclusions without listening to the point of view" of Haqqani.
Haqqani has been summoned to Islamabad to explain the issue to the country`s leadership, he said.
Gilani added that there was no problem for his coalition government as it had a "working relationship" with other national institutions.
Indicating that there were efforts being made by certain elements to dislodge his government, Gilani said any step "contrary to the law and the Constitution would not be acceptable".
Certain people yearning for a change in government through unconstitutional means would "miserably fail" as the ruling coalition is strong and stable enough to counter such moves, he added.
Haqqani has offered to resign over the situation but has denied reports of his alleged involvement in drafting the secret memo, which purportedly committed the government to creating a new national security set-up in exchange for US help in preventing a military takeover.
The Ambassador, a close aide of President Asif Ali Zardari, has played a key role in relations between Pakistan`s weak civilian government and the US administration. Zardari reportedly feared the military might seize power in the wake of the killing of Osama bin Laden in the garrison city of Abbottabad on May 2.