The men were named as Ibrahim Adam, 24, and Mohammed Azmir, 37, by their family and friends, Britain's Press Association, domestic news agency reported.
They were killed in the lawless Waziristan tribal region bordering Afghanistan at least three months ago, it reported.
"We're aware of reports and looking into them further," a Foreign Office spokesman told AFP.
A government source said that getting confirmation would take time because the area is remote.
Adam, from London, was wanted by British authorities after absconding from a government "control order" used to limit the movements of suspected extremists in May 2007.
Azmir, a father of three who lived in Ilford, a town east of London, was slapped with a finance ministry order in February 2010 freezing his assets over concerns that he was involved in funding terrorism.
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