The Pentagon on Wednesday disputed claims that two kidnapped Serbian diplomats were killed in a US air strike on an Islamic State compound in Libya.

US warplanes and drones last week pulverized a jihadist training camp near the Libyan coastal city of Sabratha, killing dozens of people including an IS operative who allegedly helped plot two deadly attacks in neighboring Tunisia.

However, Belgrade said the strike's victims also included two officials from Serbia's embassy in Libya, Sladjana Stankovic and Jovica Stepic, who had been taken hostage in the area in November.

Pentagon spokesman Captain Jeff Davis said an extensive analysis of surveillance of the IS compound and a review of photos posted online of the two Serbians' bodies yielded no evidence the man and woman were killed in the strike.

"As we've gone back looked at the photos of the Serbian citizens who died and gotten further information about the strike itself, the information we had leading up to it, (and) the assessment of the very extensive damage, it doesn't match with what is in the photos," Davis said.

"These photos didn't any have any sense of place to them, that they were clearly taken at the site of the bombing... (there's) nothing to indicate that their deaths are the result of the bombing."

Davis suggested the bodies would have been in far worse condition had they been killed in the massive air strike.

"It was not consistent with what we would expect human remains to look like following a strike of that magnitude," he said.

On Saturday, a day after the strike, Serbia blamed America for killing the two hostages, and Serbian Prime Minister Aleksandar Vucic later said the pair would have been released, had they not been killed.

The United States quickly offered its condolences but also expressed immediate doubts of the claims.

US officials said the raid likely killed Noureddine Chouchane, who along with other jihadists had been planning attacks against American and other Western interests.

Libya spiralled into chaos after longtime dictator Moamer Kadhafi was ousted and killed in October 2011, with two governments vying for power and armed groups battling to control vast energy resources.

Belgrade maintains an embassy in Tripoli, and Serbian citizens -- mostly doctors, other medical staff and construction workers -- have been working in Libya for decades due to close bilateral relations during the Kadhafi regime.