Libya's top oil official on Thursday summoned the local heads of US energy firms to tell them a diplomatic row with Washington could have a negative impact on US businesses in Libya, the state oil company said.

Libya's NOC state oil firm said in a statement its chief summoned the local representatives of Exxon Mobil, ConocoPhillips, Occidental and Marathon to complain about remarks by a US State Department official on Libyan leader Muammar Gaddafi.

Earlier, Libya summoned a US diplomat to warn that ties would suffer if Washington did not apologise for the US official's dismissive comments about Gaddafi's call for 'jihad' against Switzerland.

The Libyan Foreign Ministry said the remarks were ill informed and warned that if no apology was forthcoming, "that would have a negative impact on political and economic relations," Jana reported.

On Wednesday, the State Department spokesman sought to calm the dispute but avoided making a direct apology. "I made an off-hand comment last Friday regarding statements from Libya. It was not intended to be a personal attack," State Department spokesman P.J. Crowley told reporters.   

"That said, a call for jihad against any country or individual has the potential to harm and is not something the United States takes lightly," he said, adding that Washington reserved the right to comment on the actions of other nations.

US energy companies have invested heavily in Libya, home to Africa's largest proven oil reserves, since the country emerged from decades of international isolation. - Reuters