The militants - identified as Usman Basra, Naimutallah Uzbak, Mufti Mohsin alias Jalaluddin, Farhaj Mustafa, Rana Abdur Rehman and Muhammad - have been arrested from different parts of the Punjab province, police said.
During interrogation, the accused confessed to committing kidnappings of Shahbaz and Warren and killing Shia cleric Irfan Naqvi. Both Shahbaz and Warren are still in captivity and believed to be held in areas bordering Afghanistan.
They also confessed to the kidnapping of a businessman - Sheikh Shahid - who later earned his freedom by paying Rs 100 million ransom to them.
Police said the arrest might lead to the safe recovery of Taseer junior and the American national.