NATO enforced a no-fly zone over Libya last year in an effort to protect civilians from attacks by forces loyal to Libyan leader Moammar Gadhafi. The conflict ended with Gadhafi's death in October 2011 after he fell into rebel hands.
A report published by Human Rights Watch this week said there was evidence to suggest anti-government forces summarily executed Gadhafi supporters in the wake of the NATO airstrike that led to his capture. The circumstances surrounding Gadhafi's death remain unclear.
Victoria Nuland, a spokeswoman for the U.S. State Department, said Washington wanted Tripoli to look into any alleged war crimes committed during last year's civil war.
"We are urging the government of Libya to genuinely investigate all these (HRW) claims and to prosecute any perpetrators in a manner consistent with Libya's international obligations," she said during her regular press briefing.
Tripoli, in a war crimes case against Gadhafi's son Saif al-Islam, maintains it has the ability to prosecute former regime officials in national courts.
Nuland added that Washington was working to train legal authorities in Libya, stressing that it was "no secret that this is a fragile and very new democracy."