Sri Lanka summoned the US ambassador to demand the Department of Homeland Security drop with what the island's government said were plans to question General Sarath Fonseka over the campaign that crushed Tamil Tiger rebels.
"The Department of Homeland Security cannot confirm nor deny the existence of any investigation," department spokesman Matt Chandler said.
State Department spokesman Ian Kelly said separately that he was not familiar with the case.
Fonseka, Sri Lanka's chief of defense staff, holds US permanent residency and arrived in the United States last week to see his daughters in the central state of Oklahoma.
Foreign Minister Rohitha Bogollagama said the Department of Homeland Security, which handles US immigration, had requested that Fonseka make himself available for questioning on Wednesday.
The minister said US authorities were trying to force Fonseka to testify "as a possible source" against Sri Lankan Defense Secretary Gotabhaya Rajapakse over allegations of huma