Online daily Infolibre made the allegations last Thursday when publishing what they claim is email evidence that Aznar was to be hired as an intermediary for Spanish arms trading company EINSA.
According to the report, the email correspondence was between EINSA's director and Miguel Blesa, former president of bailed-out bank Caja Madrid and close friend of Spain's former PM.
Blesa, who is currently under investigation for alleged mismanagement at the lender, discussed Aznar's job responsibilities and sales commission in the leaked emails, Infolibre alleges.
If true, the former Spanish PM would have helped to supply weapons to late Venezuelan leader Hugo Chávez, with whom it is widely reported he had a turbulent political relationship after leaving office.
He would have also been behind a 2008 arms deal with Libyan leader Muammar Gaddafi, who Aznar once described as “an extravagant friend”.
Socialist spokesman Antonio Hernando said in a statement on Friday that the former opposition leader should give "immediate explanations" over Infolibre's "extremely serious" report.
Aznar responded by sending out his own statement in which he denied receiving “any sort of retribution or commission” or “signing a contract and carrying out the tasks”.
Spain's Prime Minister from 1996 to 2004, the right-wing leader lost his hold on power just days after the Madrid bombings in which 191 people were killed.
Aznar's Popular Party lost the 2004 general elections after he continued to blame Basque terrorist group ETA for the attack when evidence had already emerged that an Islamist group may have been involved.