A New York court served a summons last Friday at the New York residence of Major General Shavendra Silva, who is Sri Lanka's deputy permanent representative to the United Nations.
"Even with or without diplomatic privileges, I have the strength and courage and I will fight to safeguard Sri Lanka’s interest," Silva told the Colombo-based Financial Times newspaper on Monday.
He said President Mahinda Rajapakse, who was in New York last week to attend the annual UN General Assembly meetings, had directed officials to seek legal advice.
Silva was commanding officer of the 58th Division in the army which helped crush the Tamil Tiger rebels, who had waged a war for decades demanding a homeland for the Tamil ethnic minority.
"This law suit is a yet another sinister attempt by the bankrupt LTTE (Liberation Tigers of Tamil Eelam) to tarnish the hard-won victory. I will not let any person or organisation downgrade the defeat of terrorism in Sri Lanka, to which many contributed," Silva said.
The case was filed last week by the American University Washington College of Law, a centuries-old Washington college.
It is acting on behalf of Vathsala Devi and Seetharam Siva. Devi's husband and Siva's father were allegedly killed by Sri Lankan army shelling during the final weeks of the war.
The plaintiffs allege that Silva "conspired with, aided and abetted and alternatively exercised command and control over the perpetrators of torture, extrajudicial execution and fatal shelling of civilians," local media reported.
A UN panel of experts said in April that the Sri Lankan army killed most of the tens of thousands of civilian victims of the final offensive in 2009, but both sides could have been guilty of war crimes.A documentary shown on Britain's Channel Four in June said the military shelled civilian targets and showed footage of what it said were prisoner executions and the bodies of sexually assaulted Tamil Tiger fighters.