Monday evening, Mendenhall sent several messages, including: "For those of you who said you want to see Bin Laden burn in hell ... I ask how would God feel about your heart?"
Rooney said he found difficult to understand where Mendenhall was coming from without further context, the Pittsburgh Post-Gazette reported.
"I have not spoken with Rashard so it is hard to explain or even comprehend what he meant with his recent Twitter comments," Rooney said in a statement released by the team. "The entire Steelers' organization is very proud of the job our military personnel have done and we can only hope this leads to our troops coming home soon."
In another Twitter message, Mendenhall seemed to indicate doubts about the Sept. 11, 2001, terror attacks carried out by al-Qaida on the World Trade Center twin towers.
"We'll never know what really happened. I just have a hard time believing a plane could take a skyscraper down demolition style."
His other messages on the Internet site included: "I believe in God. I believe we're ALL his children. And I believe HE is the ONE and ONLY judge."
"Those who judge others, will also be judged themselves."