COLOMBO (AFP) - Sri Lanka's military commander returned home on Thursday after cutting short a visit to the United States to avoid questioning by authorities over alleged war crimes against Tamil civilians.

The foreign ministry in Colombo said the US Department of Homeland Security (DHS) had wanted to interview Sarath Fonseka about war crimes allegedly committed during the defeat of the Tamil Tiger rebels earlier this year.

"We facilitated General Fonseka's early departure ahead of his Wednesday meeting with the DHS," Sri Lanka's Foreign Minister Rohitha Bogollagama told reporters.

He said Fonseka had earlier agreed to be questioned, but the Sri Lankan government feared he would be asked to provide evidence against Defence Secretary Gotabhaya Rajapakse.

"General Fonseka is a high ranking public official and our position is that he cannot be used as a source against another high ranking official. That's incriminating," Bogollagama said.

Fonseka, who holds US permanent residency, had travelled to Oklahoma to visit his two daughters.

Gotabhaya Rajapakse, President Mahinda Rajapakse's younger brother, was previously questioned by US immigration authorities when he visited New York as part of Sri Lanka's delegation to the UN general assembly in September.

Sri Lankan troops in May killed the leaders of the Tamil Tigers, ending one of Asia's longest-running and bloodiest insurgencies, which aimed to create a separate homeland for the island's Tamil minority.

A US State Department report presented to Congress last month charged that both the government and Tamil Tigers committed serious human rights violations in the final months of the conflict.

Fonseka was mentioned in the US report, which was initially dismissed by Colombo as "unsubstantiated," although the Sri Lankan government later promised to have the charges investigated.