The US plan to interview Fonseka followed the recent publication of a US State Department dossier outlining allegations of serious rights violations by both sides towards the end of Sri Lanka's decades-old conflict with Tamil Tiger separatists.
The report, submitted to the US Congress, refers to Fonseka having overstepped his brief.
The report covered the period from January -- when fighting intensified -- until the end of May, when Sri Lankan troops defeated the Liberation Tigers of Tamil Eelam (LTTE).
Sri Lanka last week announced it was appointing a panel to investigate the allegations after initially dismissing the report as "unsubstantiated.
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Foreign Minister Rohitha Bogollagama said the US Department of Homeland Security had requested that General Sarath Fonseka, who is currently visiting his daughters in Oklahoma, make himself available for questioning on Wednesday.
"Our position is that the meeting should not take place," Bogollagama told reporters, adding that Fonseka was