The Kremlin is also pressuring the United States to modify a new section of the Conventional Forces in Europe treaty, which sets limits on troop levels.
But a section of the Status of Forces Agreement pertaining to Pentagon contractors says "primary jurisdiction falls to the government of Iraq, " the senior Defense department official said.
As part of an effort to stop the Presevo Valley rebels linking up with a similar group in nearby Macedonia, Serb forces deployed into a southern section of the buffer zone on Wednesday with NATO approval.
The Syrian Observatory for Human Rights, a UK-based activist group, said the fighting between government forces and rebel fighters was focused on a section of motorway linking the airport to the city, which has been used by the military to transport troops and supplies.
The bench could also examine Section 5 of the 1965 Voting Rights Act - a provision that forces nine US states with a history of electoral discrimination to have all changes to voting rules first approved in Washington.