American officials have said Egypt and the United Arab Emirates were behind air strikes in Libya targeting Islamist militants fighting government forces in the capital, Tripoli.
The attacks were reportedly carried out by the UAE using bases in Egypt during the battle for Tripoli's airport.
The United States and four of its European allies - France, Germany, Italy and Britain - have jointly condemned what they describe as 'outside interference' in Libya.
The joint statement also called for an immediate ceasefire in Libya.
Egypt and the UAE - both US allies - are said to have acted without consulting Washington, which is concerned that US weapons may have been used, violating agreements under which they were sold.